1,721,049 research outputs found
Investigation of Mass Transfer Phenomena and Thermodynamic Properties of new Generation Porous Particles for High-Efficient Separations in Liquid Chromatography Through Experimental and Theoretical Approaches
No full textIn the chromatographic field, the continuous need of higher column efficiency and resolution and faster analysis has led to the development of stationary phases made of ever smaller porous particles and to the use of Ultra-High Performance Chromatographic systems.
From a theoretical view point, on the one hand, kinetic factors (diffusion, eddy dispersion, mass transfer resistance, finite rate of adsorption/desorption process) directly affect the efficiency of a chromatographic separation and on the other, thermodynamic factors (adsorption equilibria) have an impact on
retention and selectivity. It is clear that in order to achieve selective, ultra-fast and high efficient separations it is of fundamental importance to study both kinetic and thermodynamic contributions.
The detailed evaluation of the different sources of band broadening of kinetic origin can be obtained through the coupling of proper models of diffusion (parallel model or effective medium theories) in porous media and experimental measurements (peak parking and van Deemter curves).
Conversely, the application of the so-called inverse method and the perturbation method allows for the estimation of thermodynamic parameters (saturation capacity, binding constants) through the construction of adsorption isotherm of both analytes and mobile phase components on a stationary phase.
The aim of this thesis has been the complete characterization of porous materials being both hydrophobic and chiral in terms of kinetic and thermodynamic values. In the first part of this work, mass transfer kinetics of columns designed for ultrafast high performance separations packed with both sub-2 μm
and sub-3 μm fully porous particles and the second generation of core-shell particles with different functionalization have been investigated. More in detail, this work has been focused on the direct comparison between SPPs and FPPs designed for both achiral (C 18 ) and chiral separations and on a review
of the most recent applications of these materials, especially in the field of high-throughput ultrafast enantioseparations in liquid (LC) and supercritical fluid chromatography (SFC).In the second part, the study of thermodynamic properties of porous materials has been carried out on different stationary phases: chiral (Teicoplanin, Whelk-O1 and Polysaccharide) designed for ultrafast chromatography, achiral
(C 8 , C 18 ) designed for preparative chromatography and a resin designed for affinity chromatography.
The acquired information are needed to possibly correlate chemico-physical properties of porous particles (specific loading, particle type and geometry, surface area, etc.) to kinetic (adsorption-desorption kinetics, column efficiency, etc.) and thermodynamic quantities (binding constants, saturation capacities,
etc.). Moreover, thermodynamic studies may be useful for the prediction of the adsorption behavior of products of pharmaceutical interest, leading to the investigation of the feasibility of purification process through preparative and affinity chromatography.
This thesis is the result of two periods of research spent at ETH Zürich (Switzerland) and at University of Pécs (Hungary) and various national and international collaborations with Prof. Gasparrini (University of Rome, “La
Sapienza”, Italy) and Prof. Chankvetadze (University of Tbilisi, Georgia) for chiral chromatography, Prof. Felinger (University of Pécs, Hungary) for SFC, Prof. Morbidelli (ETH Zürich, Switzerland) and Fresenius Kabi iPSUM (Villadose, Rovigo, Italy) for affinity and preparative chromatography.In campo cromatografico la richiesta continua di elevate efficienze, risoluzione e analisi veloci ha portato allo sviluppo di fasi stazionarie costituite da particelle di diametro sempre più ridotto e all’utilizzo di strumenti cromatografici ultra performanti. Da un punto di vista teorico, da un lato, i fattori cinetici (diffusione, dispersione eddy, resistenza al trasferimento di massa, velocità finita del processo di dsorbimento/desorbimento) influenzano direttamente l’efficienza di una separazione cromatografica e dall’altro, fattori termodinamici (equilibri di adsorbimento) hanno un effetto su ritenzione e selettività.
Per ottenere separazioni selettive, ultra veloci e altamente efficienti è quindi fondamentale studiare sia i contributi cinetici che termodinamici. La valutazione dettagliata delle differenti sorgenti di allargamento di banda di origine cinetica può essere effettuata attraverso l’accoppiamento di opportuni modelli di diffusione
nei mezzi porosi (modello parallelo o effective medium theories) e misure sperimentali (peak parking e curve di van Deemter). Al contrario, l’applicazione del metodo inverso e del metodo delle perturbazioni permette la stima di parametri termodinamici (capacità di saturazione, costanti di binding) attraverso lo studio di isoterme di adsorbimento sia di analiti che di componenti della fase mobile adsorbiti sulla fase stazionaria.
Lo scopo di questo lavoro di tesi è stato la completa caratterizzazione di materiali porosi, sia di tipo idrofobico che chiarle, in termini di valori cinetici e termodinamici. Nella prima parte del lavoro sono state indagate le cinetiche di trasferimento di massa di colonne progettate per separazioni ultra veloci e ad alta efficienza impaccate con particelle totalmente porose (FPP) con diametro sub-2 μ m e sub-3 μ m e con la seconda generazione di particelle superficialmente porose (SPP) con diversa funzionalizzazione. Più precisamente, questo lavoro è stato focalizzato nel confronto diretto tra SPP e FPP utilizzate per separazioni
achirali e chirali e su una review riguardante le applicazioni più recenti per questi materiali con un maggiore dettaglio nel campo di separazioni enantiomeriche ultra veloci ad alta produttività ed efficienza in cromatografia liquida (LC) e a fluido supercritico (SFC). Nella seconda parte della tesi lo studio delle proprietà termodinamiche di materiali porosi è stato effettuato su diverse fasi stazionarie: chirali (teicoplanina, Whelk-O1 e polisaccaridiche) progettate per cromatografia ultra veloce, achirali ( C 8 e C 18 ) progettate per
cromatografia preparativa e una resina progettata per cromatografia di affinità.Le informazioni ottenute sono necessarie per poter correlare le proprietà chimico-fisiche delle particelle porose (quantità di selettore presente, tipo e geometria delle particelle, area superficiale, ecc.) alle quantità cinetiche (cinetiche di adsorbimento-desorbimento, efficienza di colonna, ecc.) e termodinamiche (costanti di binding, capacità di saturazione, ecc.). Inoltre studi termodinamici potrebbero essere utili per predire il comportamento
di adsorbimento di prodotti di interesse farmaceutico, rendendo così possibile lo studio dell’attuabilità del processo di purificazione attraverso la cromatografia preparativa e di affinità.
Questa tesi è il risultato di due periodi di ricerca effettuati in istituzioni estere svolti presso l’ETH di Zurigo (Svizzera) e presso l’Università di Pécs (Ungheria) e di numerose collaborazioni nazionali e internazionali con il Prof. Gasparrini (Università di Roma, “La Sapienza”, Italia) e il Prof. Chankvetadze (Università di Tbilisi, Georgia) per quanto concerne la cromatografia chirale, il Prof. Felinger (Università di Pécs, Ungheria) per
cromatografia a fluido supercritico, il Prof. Morbidelli (ETH di Zurigo, Svizzera) e Fresenius Kabi iPSUM (Villadose, Rovigo, Italia) per cromatografia di affinità e preparativa
Enhancing the purification of crocin-I from saffron through the combination of multicolumn countercurrent chromatography and green solvents
No full textCrocin-I, a valuable natural compound found in saffron (Crocus sativus L.), is the most abundant among the various crocin structures. Developing a cost-effective and scalable purification process to produce high-purity crocin-I is of great interest for future investigations into its biological properties and its potential applications in the treatment of neurological disorders. However purifying crocin-I through single-column preparative chromatography (batch) poses a yield-purity trade-off due to structural similarities among crocins, meaning that the choice of the collection window sacrifices either yield in benefit of higher purity or vice versa. This study demonstrates how the continuous countercurrent operating mode resolves this dilemma. Herein, a twin-column MCSGP (multicolumn countercurrent solvent gradient purification) process was employed to purify crocin-I. This study involved an environmentally friendly ethanolic extraction of saffron stigma, followed by an investigation into the stability of the crocin-I within the feed under varying storage conditions to ensure a stable feed composition during the purification. Then, the batch purification process was initially designed, optimized, and subsequently followed by the scale-up to the MCSGP process. To ensure a fair comparison, both processes were evaluated under similar conditions (e.g., similar total column volume). The results showed that, at a purity grade of 99.7%, the MCSGP technique demonstrated significant results, namely + 334% increase in recovery + 307% increase in productivity, and - 92% reduction in solvent consumption. To make the purification process even greener, the only organic solvent employed was ethanol, without the addition of any additive. In conclusion, this study presents the MCSGP as a reliable, simple, and economical technique for purifying crocin-I from saffron extract, demonstrating for the first time that it can be effectively applied as a powerful approach for process intensification in the purification of natural products from complex matrices
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
On the effect of chiral selector loading and mobile phase composition on adsorption properties of latest generation fully- and superficially-porous Whelk-O1 particles for high-efficient ultrafast enantioseparations
No full textThe adsorption isotherms of trans-stilbene oxide (TSO) enantiomers have been measured under a variety of normal phase (NP) mobile phases (MPs) on three Whelk-O1 chiral stationary phases (CSPs), prepared respectively on 1.8 μm and 2.5 μm fully porous particles (FPPs) and 2.6 μm superficially porous particles (SPPs). Specific loading of chiral selector (moles per square meter) of the two FPPs was about 20% smaller than that of SPPs (even if they were prepared under exactly the same experimental conditions). Regardless of particle size or format, adsorption was described by means of a Bilangmuir model with ethanol/hexane MPs. On the other hand, in pure hexane, the Tóth isotherm was employed. Interestingly, it was found that selective and nonselective Henry's constants vary in opposite directions by increasing the percentage of strong MP modifier (between 3 and 10%, v/v). Saturation capacity of SPPs (referred only to the porous zone of the particle) was remarkably smaller than those of FPPs. On the other hand, binding constants on both selective and nonselective sites were significantly larger on SPPs. Finally, a correlation between the specific loading of chiral selector and the binding constants of enantiomers was suggested by data, which can be important also to understand the kinetic behavior of these particles in chiral ultrafast applications
Effective and Practical Stereoselective Synthesis of Nutlins Precursors by Immobilization of Privileged Chiral Mono‐Amidine Catalyst
No full textA strategy for the immobilization of Johnston's Mono(AMidine) catalyst (MAM) onto polystyrene, silica and hybrid silica-polystyrene nanoparticles is presented. The catalyst activity was evaluated in the stereoselective aza-Henry reaction leading to the pivotal β-amino nitroalkane precursors of the anti-cancer agents Nutlins (with Nutlin-3a as the most active drug). The effect of the support and the linker on the catalytic performance was investigated, observing an interesting match/mismatch effect when using a chiral linker. The polystyrene-supported 3-pyrrolidinol-linked PS-(S)-Pyr-MAM organocatalyst showed the best activity among the tested catalysts, behaving very similarly to the homogeneous counterpart in the synthesis of a library of Nutlins precursors: yield up to 95%, ee up to 99%, and dr up to >99:1. The catalyst recyclability was also assessed through simple filtration, yielding a satisfactory 93% ee after 5 cycles, showing only a moderate decrease in conversion efficiency (c..
Recent advancements and future directions of superficially porous chiral stationary phases for ultrafast high-performance enantioseparations
No full textThis review focuses on the use of superficially porous particles (SPPs) as chiral stationary phases for ultra-high performance liquid enantioseparations. In contrast to what happened in achiral separations where core–shell particles invaded the market, the introduction of SPPs in chiral liquid chromatography (LC) has been relatively recent. This is due in part to the technical difficulties in the preparation of these phases, and in part to scarce understanding of mass transfer phenomena in chiral chromatography. As a matter of fact, nowadays, the development of superficially porous CSPs is still in its infancy. This paper covers the most recent advancements in the field of core–shell technology applied to chiral separations. We review the kinds of chiral selectors that have been used for the preparation of these phases, by discussing the advantages of chiral SPPs over their fully-porous counterparts for high efficient high throughput enantioseparations. Notwithstanding the apparently obvious advantages in terms of the mass transfer of chiral SPPs, some critical aspects that could impact their development are presented
Recent developments in the high-throughput separation of biologically active chiral compounds via high performance liquid chromatography
No full textBioactive compounds, including active pharmaceutical ingredients (APIs), are often chiral molecules where stereoisomers have different biological and therapeutic activity. Nevertheless, the preparation of these molecules can lead to racemic or scalemic mixtures (it is not trivial to produce just the optically pure compound). The evaluation of the enantiomeric purity of bioactive compounds, and therefore quality, is indeed of fundamental importance for regulatory scopes. Chiral high performance liquid chromatography (HPLC) is the gold standard technique to separate and to purify enantiomers. This comes from the wide availability of commercial chiral stationary phases (CSPs) and operational modes, which makes the technique extremely versatile. In recent years, the most relevant trend in the field of chiral analytical HPLC has been the development of CSPs suitable for fast or even ultrafast separations, thus favoring the high throughput screening of biologically active chiral compounds. This process has somehow lagged behind compared to achiral HPLC, due to a series of practical and fundamental issues. The experience has shown how in chiral chromatography even very basic concepts, such as the supposed kinetic superiority of core-shell (pellicular) particles over fully porous ones to improve the chromatographic efficiency, cannot be taken for granted. In this review, the most relevant fundamental and practical features that must be taken into consideration to design successful high-throughput, fast enantioseparations will be discussed. Afterwards, the main classes of CSPs and the most relevant, recent (last five-year) high-throughput applications in the field of the separation of chiral bioactive compounds (for pharmaceutical, forensic, food, and omics applications) will be considered
Sustainable cannabinoids purification through twin-column recycling chromatography and green solvents
No full textIn the present study, twin-column recycling chromatography has been employed for the purification of a Cannabis extract by using a green solvent, ethanol, as the mobile phase. In particular, the complete removal of the psychoactive tetrahydrocannabinol (THC) from a Cannabis extract rich in cannabidiol (CBD) was achieved under continuous conditions. The performance of the method, in terms of compound purity, recovery, productivity and solvent consumption, was compared to that of traditional batch operations showing the potential of the twin-column recycling approach. The employment of a theoretical model to predict the band profiles of the two compounds during the recycling process has facilitated method development, thus further contributing to process sustainability by avoiding trial and error attempts or at least decreasing the number of steps significantly
Integrated multidimensional chromatography on preparative scale for oligonucleotides purification
No full textTherapeutic oligonucleotides represent a recent breakthrough in the pharmaceutical industry due to their ability to regulate gene expression with great specificity. This aspect allows treatment of a wide range of diseases. However, since oligonucleotides are used for therapeutic purposes, the Active Pharmaceutical Ingredient (API) must fulfill strict purity levels which require intensive purification steps. For oligonucleotides, and biomolecules in general, preparative liquid chromatography is the technique of choice to perform large scale purifications, typically in batch mode, i.e. using a single column. Specifically, since ONs are mainly large, hydrophilic and charged molecules, Anion Exchange chromatography (AEX) and Ion Pair Reversed Phase chromatography (IPRP) are the preferred chromatographic modes for their downstream processing. Nevertheless, these approaches suffer from a purity-yield trade-off, and for this reason, more than one purification step is usually required. The two chromatographic modes can therefore be used consequently to remove different groups of impurities, thanks to their orthogonality. In this work, a multidimensional and orthogonal approach on a (semi)preparative scale, namely "Integrated Batch process", was applied for the purification of a single-stranded DNA oligonucleotide. This process combines two chromatographic steps without any hold step, operator intervention or sampling of the first step. The performance parameters of the Integrated Batch were compared to those obtained in the single batch runs under different experimental conditions (chromatographic mode, eluent systems), showing the potential of this integrated approach. This proof-of-concept study illustrates how this technique can considerably reduce overall production time and how it allows to increase the robustness and reproducibility of the method, since the process is highly automated
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