197,452 research outputs found
Optimal operation of simulated moving-bed units for non-linear chromatographic separations - II. Bi-Langmuir isotherm
No full textSeveral important theoretical results have been previously obtained to predict the behaviour of continuous chromatographic separation units in the case of Langmuirian type of isotherms. Concerning separation of binary mixtures in a non-adsorbable carrier with SMB units, stoichiometric and non-stoichiometric Langmuir and modified Langmuir have been considered in the frame of equilibrium theory. For these isotherms explicit constraints on the operating parameters have been found to achieve complete separation (M. Mazzotti, G. Storti, M. Morbidelli, J. Chromatogr. A 769 (1997) 3; M. Mazzotti, G. Storti, M. Morbidelli, AIChE J, 42 (1996) 2784; M. Mazzotti, M. Pedeferri, M. Morbidelli, in: Chiral Europe '96 Symposium, Spring Innovations Limited, Stockport, UK, 1996); the design of the SMB unit was then reduced to the analysis of the so-called region of complete separation for the operating parameters. In this paper, the same result is presented for the bi-Langmuir case, which can avoid the constant selectivity limit of the Langmuir isotherms. Langmuir and bi-langmuir isotherms fitting the same set of data taken from the literature were then used here to show the difference in the prediction of the region of complete separation. Finally an analysis of non-linearity effects on performance parameters is presented as a useful criterion for optimization of the separation performances. (C) 1998 Elsevier Science B.V
"Effect of Temperature on High Shear-Induced Gelation of Charge-Stabilized Colloids without Adding Electrolytes"
No full textWe demonstrated previously (Wu, H.; Zaccone, A.; Tsoutsoura, A.; Lattuada, M.; Morbidelli, M. Langmuir 2009,25, 4715) that, for a colloid stabilized by charges from both polymer chain-end groups and adsorbed sulfonate surfactants, when the surfactant surface density reaches a certain critical value, the shear-induced gelation becomes unachievable at room temperature, even at an extremely large Peclet number, Pe = 4.6 x 10(4). This is due to the presence of the short-range, repulsive hydration force generated by the adsorbed surfactant. In this work, we investigate how such hydration force affects the shear-induced gelation at higher temperatures, in the range between 303 and 338 K. It is found that a colloidal system, which does not gel at room temperature in a microchannel at a fixed Pe = 3.7 x 10(4), does gel when temperature increases to a certain value. The critical initial particle volume fraction for the gelation to occur decreases as temperature increases. These results indicate that the effect of the hydration force oil the gelation decreases as temperature increases. Moreover, we have observed that at the criticality only part of the primary particles is converted to the gel network and the effective particle volume fraction forming the gel network does not change significantly with temperature. The effective particle volume fraction is also independent of the surfactant surface coverage. Since the effective particle volume fraction corresponds to space filling requirement of a standing gel network, which is mainly related to the clusters structure, this result indicates that at a given shear rate the Cluster structure does not change significantly with the surfactant Surface coverage. Oil the other hand, since the cluster morphology is a strong function of the shear rate, we have observed that when the Peclet number is lowered from Pe = 3.7 x 10(4) to 1.7 x 10(4), the effective particle Volume fraction reduces from 0.19 to 0.12 at 3 13 K
Multicolumn Countercurrent Solvent Gradient Purification (MCSGP) process for the intensification of the polishing step of a bioactive peptide mixture
No full textPharmaceutical products, including peptides, must satisfy very strict purity specifications, because
of quality and safety reasons. Therefore, the necessity to operate one or more purification steps to
obtain high quality drugs is indisputable. Critical impurities chemically very similar to the target
product are generated during the synthesis and are generally removed by means of preparative
single-column chromatographic techniques (=batch methods) [1,2]. Batch methods struggle to
separate completely the peptide of interest from other groups of impurities, because of their
similarity and of high loading of sample processed in preparative conditions, which cause peaks
overlapping [3]. The typical situation encountered in these cases is the so-called center-cut
separation, where the target elutes as intermediate between two other groups of impurities less and
more retained respectively. The direct consequence of this apparently insurmountable overlapping
is a yield-purity trade-off, a limit intrinsic to batch chromatography according to which it is possible
to obtain either high purity or high recovery of the peptide of interest, depending on whether the
overlapping windows are collected or not [4]. This trade-off leads to drawbacks in the overall
economy of the process. Multicolumn chromatographic processes, operating in continuous and
countercurrent mode, can alleviate this limitation by performing internal recycling of the
overlapping portions of the chromatogram [5]. The technique used in the frame of this research is
twin-column Multicolumn Countercurrent Solvent Gradient Purification (MCSGP), which has been
applied to the purification of an industrial crude of a bioactive decapeptide. It has been
demonstrated that MCSGP leads to promising results, including a remarkable improvement in
process performance (up to 6 times higher) from the point of view of recovery, productivity and
solvent consumption, with respect to the corresponding batch run. The automation of the process on
industrial scale would lead to great reproducibility which would reflect in improved consistency in
product quality.
[1] C. De Luca; S. Felletti; G. Lievore; A. Buratti; S. Vogg; M. Morbidelli; A. Cavazzini; M.
Catani; M. Macis; A. Ricci; W. Cabri, J Chromatogr A 2020, 1625, 1-7.
[2] C. De Luca; S. Felletti; G. Lievore; T. Chenet; M. Morbidelli; M. Sponchioni; A. Cavazzini; M.
Catani, Trends Analyt Chem 2020, 132, 1-8.
[3] S. Vogg; N. Ulmer; J. Souquet; H. Broly; M. Morbidelli, Biotechnol J 2019, 1800732, 1-8.
[4] T. Müller-Späth; G. Ströhlein; O. Lyngberg; D. Maclean, Chem Today 2013, 31, 56-60.
[5] F. Steinebach; T. Müller-Späth; M. Morbidelli, Biotechnol J 2016, 11, 1126-1141
Process intensification of the polishing step of a bioactive peptide through Multicolumn Countercurrent Solvent Gradient Purification
No full textPharmaceutical products, including peptides, must satisfy very strict purity specifications, because of quality and safety reasons. Therefore, the necessity to operate one or more purification steps to obtain high quality drugs is indisputable. Critical impurities chemically very similar to the target product are generated during the synthesis and are generally removed by means of preparative single-column chromatographic techniques (=batch methods) [1,2]. Batch methods struggle to separate completely the peptide of interest from other groups of impurities, because of their similarity and of high loading of sample processed in preparative conditions, which cause peaks overlapping [3]. The typical situation encountered in these cases is the so-called center-cut separation, where the target elutes as intermediate between two other groups of impurities less and more retained respectively. The direct consequence of this apparently insurmountable overlapping is a yield-purity trade-off, a limit intrinsic to batch chromatography according to which it is possible to obtain either high purity or high recovery of the peptide of interest, depending on whether the overlapping windows are collected or not [4]. This trade-off leads to drawbacks in the overall economy of the process. Multicolumn chromatographic processes, operating in continuous and countercurrent mode, can alleviate this limitation by performing internal recycling of the overlapping portions of the chromatogram [5]. The technique used in the frame of this research is twin-column Multicolumn Countercurrent Solvent Gradient Purification (MCSGP), which has been applied to the purification of an industrial crude of a bioactive decapeptide. It has been demonstrated that MCSGP leads to promising results, including a remarkable improvement in process performance (up to 6 times higher) from the point of view of recovery, productivity and solvent consumption, with respect to the corresponding batch run. The automation of the process on industrial scale would lead to great reproducibility which would reflect in improved consistency in product quality.
References
[1] De Luca, C.; Felletti, S.; Lievore, G.; Buratti, A.; Vogg, S.; Morbidelli, M.; Cavazzini, A.; Catani, M.; Macis, M.; Ricci, A.; Cabri, W. J Chromatogr A 2020, 1625, 1-7.
[2] De Luca, C.; Felletti, S.; Lievore, G.; Chenet, T.; Morbidelli, M.; Sponchioni, M.; Cavazzini, A.; Catani, M. Trends Analyt Chem 2020, 132, 1-8.
[3] Vogg, S.; Ulmer, N.; Souquet, J.; Broly, H.; Morbidelli, M. Biotechnol J 2019, 1800732, 1-8.
[4] Müller-Späth, T.; Ströhlein, G.; Lyngberg, O.; Maclean, D. Chem Today 2013, 31, 56-60.
[5] Steinebach, F.; Müller-Späth, T.; Morbidelli, M. Biotechnol J 2016, 11, 1126-1141
Patchy Colloidal Particles Via Surfactant Adsorption: Interactions and Gels of Tunable Structure
No full textThe presence of charged molecules attached on the surface of Brownian particles can dramatically affect their mutual interaction as well as their interactions with foreign surfaces. With respect to aggregation, the coexistence of domains of charged adsorbed molecules and hydrophobic domains on polymer colloids opens up the possibility of tuning the interactions in a wide range from homogeneously hydrophobic surfaces to completely hydrophilic repulsive surfaces with strong hydration forces. In a well characterized system made of styrene-acrylate copolymer particles and two different ionic surfactants, aliphatic C-18 carboxylate and aliphatic C-15 sulfonate, we have shown experimentally by means of laser light scattering that an initial, gas-like state of noninteracting adsorbed molecules laying down to the particle surface is followed, with increasing surfactant concentration, by the formation of condensed domains prior to reaching full coverage of the particle surface. In the low salt limit, by shearing the dispersion at very high shear-rate in a microchannel, it is shown that the surfactant domains on two particles can fuse/adhere leading to aggregation as long as an even small-sized uncovered polymer patch is present and aggregation is always possible on the free hydrophobic polymer patches. In the case of fully developed films, by analyzing the mechanism of shear aggregation in the low-salt limit theoretically, we show that short-range hydration repulsive forces dominate over DLVO forces and adhesion/aggregation can never be achieved even upon application of extremely high collision energies. We can also provide evidence that gels obtained by shearing the dispersion at high-shear rate at low-salt exhibit a structure that is strongly affected by the degree of coverage of surfactant, i.e. by the relative extension of charged-hydrophilic to hydrophobic patches. The fractal dimension of the gel can indeed vary from 2.1 at high surfactant coverage where only a few small patches are available for aggregation (valence-limited case) to 2.8 at low surfactant coverage where the gel is made of very compact clusters. This finding unfolds new possibilities for making engineered mesoscopic disordered materials by tuning the surface properties at microscopic level.
Zaccone, Wu, Lattuada and Morbidelli, Journal of Physical Chemistry B, 112, 1976 (2008)
Zaccone, Wu, Lattuada and Morbidelli, Journal of Physical Chemistry B, in pres
Conferimento del premio intitolato ad Aldo M. Sandulli
No full text- Aldo M. Sandulli e il suo contributo alla certezza del diritto e alla unificazione ordinamental
Mechanism of Adsorption of Anionic Surfactants on the Surface of Functionalized Nanoparticles
No full textThe mechanism of adsorption of amphiphillic molecules on the surface of Brownian particles is essential for understanding and controlling the stability of functionalized nanoparticles, which are nowadays used in a broad range of fields, such as semiconductor, drug delivery system and catalysis. In this work, we have used light scattering (LS) techniques combined with determination of adsorption isotherms, as developed previously in our lab1, to study the adsorption mechanism of anionic surfactants on the heterogeneous surface of particles consisting of a rubber core surrounded by a plastic shell. Particles with the same mass of the core but different masses of the shell have been used. The adsorption isotherms for the different particles have been obtained by surface tension measurements both before and after removal of the particles by centrifugation. At the same time, the shell thickness and the related change of the particle radius during the surfactant adsorption have been evaluated by LS. The evaluation of the radius of the particle, of the hydrodynamic radius, and of the gyration radius by LS (both static and dynamic) provided significant indications about the particle shape. Cryo-SEM images of the particles gave further evidence about their morphology. For pure rubber spheres, the information on the change of the particle radius obtained from LS confirmed the two-stage adsorption mechanism previously proposed for the adsorption on larger particles1 : at the beginning the surfactant molecules adsorb in a ?head to tail? way in order to maximize the hydrophobic interactions between the surface and the hydrocarbon tail; with the increase of the surfactant concentration on the surface, the molecules assume a ?tails on? disposition. However, for the particles with a partial polymeric shell surrounding the rubber core, the adsorption mechanism becomes more complicated. From the experimental data, the ratio of exposed surface of the rubber core to the total external surface has been calculated. A model has been developed, which is based on combining information about the adsorption of the same surfactant on the pure rubber core and pure shell materials measured indipendently, to describe the partitioning of the surfactant on different material surfaces. Starting from this clear picture of the adsorption mechanism, the colloidal stability of these particles both under shear and stagnant conditions has been investigated. For all the particles the turbulent coagulation was studied by shearing the dispersions in a micro channel at very high shear-rate and varying temperature and particle concentration. The conversion of the primary particles as well as the cluster size of the obtained gel were evaluated by Small Angle Light Scattering. The gel samples were also characterized in terms of rheological properties and by taking SEM pictures. Combination of several techniques allowed the understanding of the influence of the surface morphology on the particles interactions.
References:
[1] A. Zaccone, H. Wu, M. Lattuada and M. Morbidelli, Journal of Physical Chemistry B; 2008, 112, 197
Dynamic response studies on aggregation and breakage dynamics of colloidal dispersions in stirred tanks
No full textAggregation and breakage of aggregates of fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tanks using small-angle static light scattering. It was found that the steady-state values of the root-mean-square radius of gyration are fully reversible upon changes of stirring speed as well as solid volume fraction. Steady-state values of the root-mean-square radius of gyration were decreasing with decreasing solid volume fraction as well as with increasing stirring speed. Moreover, it was found that the steady-state structure and shape of the aggregates is not influenced by the applied stirring speed
General model for the achiral chromatography of enantiomers forming dimers: application to binaphthol
No full textThis works deals with the development of a model for the description of the chromatographic behavior of enantiomers forming dimers on achiral stationary phases. The model describes the formation of both homochiral and heterochiral dimers by introducing two equilibrium constants, Khomo and Khetero, which have to be independently estimated. The adsorption of both monomeric and dimeric species is described by a bi-Langmuir isotherm. Both adsorption and dimerization equilibrium models are implemented in a standard equilibrium-dispersive model of the chromatographic column. The isotherm parameters are determined by fitting of pulses constituted either of the pure enantiomers or of non racemic mixtures of both enantiomers. The validity of the model is then assessed by application to the binaphthol case. © 2003 Elsevier B.V. All rights reserved
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Book Review: The Solar System Beyond Neptune, M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, A. Morbidelli (Eds.)
No full textBook Review: The Solar System Beyond Neptune, M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, A. Morbidelli (Eds.). Tucson, Arizona: The University of Arizona Press (2008).The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202
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