1,721,007 research outputs found
Transphosphatidylation of phospholipids in presence of ionic liquids
No full textNatural and synthetic phospholipids (PLs) have attracted considerable interest for the multiple scientific and practical applications which follow from their amphiphilic properties. PLs are the focus of biomedical research because of their possible use as pharmaceuticals, food additives, cosmetics, in liposome technology, in gene transfer therapy and in drug delivery systems. However, the investigations and applications rely upon the availability of a great number of purified PLs which can be obtained by semisynthesis from natural sources or from synthetic precursors. The aim of this work is to investigate innovative reaction media such as ionic liquids (ILs) for enzymatic PLs transformations in order to obtain a higher selectivity in the enzymatic transphosphatidylation reactions of natural phosphatidylcholine catalyzed by phospholipase D (PLD) from Streptomyces PMF. We have tested the stability and the activity of this PLD in various commercial ILs. We illustrate the encouraging preliminary results of the use of ILs as co-solvents in transesterification reactions with different alcohols. The presence of ILs seems to drive the reaction towards transphosphatidylation with high depression of competitive hydrolysis. We believe that the results here illustrated can stimulate further study on PLs biotransformations in ILs
Synthesis and Application of Cellulose-Polyethyleneimine Composites and Nanocomposites: A Concise Review
Full text linkCellulose/polyethyleneimine composites have increasingly attracted the attention of scientific community, devoted to the design and development of new synthetic strategies and materials for different application fields. In this review, after introducing the main characteristics of the two polymeric components, we provide in the second section a critical overview on the main protocols for the synthesis of these composites, considering both the several cellulose sources and forms, and the different cross-linkers and cross-linking procedures developed for this purpose, outlining advantages and limits for the reported approaches. The last section analyses the principal results obtained in different application fields. A wide discussion is dedicated to the principal use of cellulose/polyethyleneimine composites as sorbents for water remediation from heavy metal ions and organic contaminants. Subsequently, we introduce the literature describing the use of these composites, functionalized appropriately, where necessary, as drug delivery systems, sensors, and heterogeneous catalysts for organic reactions. Finally, after a brief description of other random applications, we furnish a personal analysis of actual limits and potentialities for these systems
Silver Nanoparticles for Water Pollution Monitoring and Treatments: Ecosafety Challenge and Cellulose-Based Hybrids Solution
Full text linkSilver nanoparticles (AgNPs) are widely used as engineered nanomaterials (ENMs) in many advanced nanotechnologies, due to their versatile, easy and cheap preparations combined with peculiar chemical-physical properties. Their increased production and integration in environmental applications including water treatment raise concerns for their impact on humans and the environment. An eco-design strategy that makes it possible to combine the best material performances with no risk for the natural ecosystems and living beings has been recently proposed. This review envisages potential hybrid solutions of AgNPs for water pollution monitoring and remediation to satisfy their successful, environmentally safe (ecosafe) application. Being extremely efficient in pollutants sensing and degradation, their ecosafe application can be achieved in combination with polymeric-based materials, especially with cellulose, by following an eco-design approach. In fact, (AgNPs)-cellulose hybrids have the double advantage of being easily produced using recycled material, with low costs and possible reuse, and of being ecosafe, if properly designed. An updated view of the use and prospects of these advanced hybrids AgNP-based materials is provided, which will surely speed their environmental application with consequent significant economic and environmental impact
L-Amino acid amides via dynamic kinetic resolution
No full textIn recent evaluations of chemical processes trying to comply to the rule of GMF and green chemistry, amide bond formation was identified as one of the most utilized and problematic synthetic step in the pharmaceutical industry. From a detailed study it was found that N-acylation reactions for amide formation were used in more than 50% of current synthesis of drug candidates.
We have recently developed an efficient methodology for the amidation of N-protected amino acid thioesters under Dynamic Kinetic Resolution (DKR) conditions, where the relatively high acidity of the α-hydrogen was exploited in a base-catalysed substrate racemization occurring in the same pot with a selective, protease-mediated, amidation.
The amides are obtained with high optical purity and high chemical yield by ammoniolysis or aminolysis catalyzed by CLEA-AlcalaseTM starting from the relative thioester, in presence of a racemizing strong organic base (DBU) and a nitrogen nucleophile in tert-butanol with controlled water activity. The reaction is carried out under kinetic control, and different parameters such as amine concentration, base ratio, water content, enzyme amount have been checked for the success of the DKR process
Development of acid-free chitosan films in food coating applications: Provolone cheese as a case study
Full text linkChitosan has been extensively explored in food coatings. Still, its practical application is largely hampered by its conventional wet processing in acetic acid, whose residuals negatively impact food quality and safety. Here, we propose a new method to formulate chitosan coatings for food applications by avoiding organic acid processing and validate them on a cheese model. The procedure entails modifying a previously reported process based on HCl chitosan treatment and neutralising the resulting gel. The obtained chitosan is solubilised in water using carbonic acid that forms in situ by dissolving carbon dioxide gas. The reversibility of water carbonation allows for easy removal of carbonic acid residues, resulting in acid-free chitosan films and coatings. The performance of the coating was tested against state-of-the-art chitosan-based and polymeric coatings. We preliminarily characterised the films' properties (water stability, barrier, and optical properties). Then, we assessed the performance of the coating on Provolone cheese as a food model (mass transfer and texture profiles over 14 days). The work demonstrated the advantage of the proposed approach in solving some main issues of food quality and safety, paving the way for an effective application of chitosan in future food contact applications
A METABOLIC-LIKE CYCLE FOR SYNTHETIC APPLICATIONS
Full text linkSystems Biocatalysis is a new approach consisting of organizing enzymes in vitro to generate an artificial metabolism for synthetic purposes. The interconversion of functional groups is the main objective of biocatalysis, and systems organizing a series of enzymes to achieve a multi-step reaction have been reported. The assembly of essentially the same enzymes utilized in Nature to drive the transformation of carbohydrates towards useful synthetic intermediates [1] has been referred to as an artificial metabolism. SysBiocat aims at a similar goal addressing the generalization and organization of group of enzymes (a tool-box) able to perform a series of reactions of general synthetic utility where the feasibility is connected with the obtainment of enzymes of wide substrate specificity or in a rich array of variable common catalytic functions. [2] As a demonstration of this concept, we have recently assembled a biochemical like cycle (Asp-cycle) connecting among them an unsaturated carboxylate (fumaric acid), an alpha-amino acid (L-aspartic acid), a keto acid (oxalacetic acid) and the corresponding alpha-hydroxyacid (D- or L-malic acid). [3]
In this view, the obtained cycle may be exploited by coupling it with synthetically relevant reactions which are driven to completion thanks to one or more irreversible steps in the reaction sequence.
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[1] W.D. Fessner, C. Walter, “Artificial metabolism”, Angew Chem Int Ed, 1992, 31, p. 614
[2] U. T. Bornscheuer, G. W. Huisman, R. J. Kazlauskas, S. Lutz, J. C. Moore, K. Robins, “Engineering The Third Wave Of Biocatalysis”, Nature, 2012, 485, p. 185
[3] D. Tessaro, L. Pollegioni, L. Piubelli, P. D’Arrigo, S. Servi, “Systems Biocatalysis: An Artificial Metabolism for Interconversion of Functional Groups”, ACS Catalysis, 2015, 5, p. 160
Development of a Generalised Equilibrium Modified Atmosphere Model and its Application to the Taleggio Cheese
Full text linkThe food metabolic processes influence the gas composition of packaged products: by finely tuning the gas fluxes through the packaging, the aerobic and anaerobic respiration processes can be efficiently exploited to regulate the equilibrium gas concentrations. In this work, we present a generalised model able to predict the evolution of gases in micro-perforated equilibrium MAP, with a detailed evaluation of fluxes through the perforations by means of Computational Fluid Dynamics. It was found that the Sherwood number for the studied micro-perforations is 0.715 and it was confirmed via experiments on packaging with oxygendepleted atmospheres. The kinetic model was experimentally validated on a smear short-ripened soft cheese (Taleggio) whose complex surface microbiota confer to the product a non-trivial respiration behaviour. Cheese slices were packed with three different micro-perforated solutions (one 120 μm diameter hole, two 90 μm diameter holes, and five 90 μm diameter holes) achieving three different equilibrium gas compositions with good model predictions. The model was applied to literature data with success, thus the model can be deemed general and applicable to many different systems
Effect of hydration on the H-bond dynamics of adsorbed water in cellulose/polyethyleneimine nano-sponges probed by 2D-COS and PCMW2D two-dimensional FTIR correlation spectroscopy
No full textIn this work, generalized (2D-COS) and perturbation-correlation moving window (PCMW2D) two-dimensional correlation analyses were applied on a set of hydration-dependent Fourier Transform Infrared Spectroscopy in Attenuated Total Refectance Geometry (FTIR-ATR) data of cellulose nano-sponges (CNSs) consisting of TEMPO-oxidized cellulose nanofbrils (TOCNF) as three-dimensional
scafolds, and branched polyethyleneimine (bPEI) as cross-linker. The aim was to get insights, starting from the computation of synchronous (SCMs)
and asynchronous (ACMs) 2D-COS and PCMW2D correlation maps, into the efect of hydration on the hydrogen bond (H-bond) dynamics of water molecules closely attached to the cellulose nanofbrils (interfacial water), based on the assessment of the complex sequence of events afecting the O–H modes
of the CNS material at diferent bPEI:TOCNF (w/w) ratios. The possibility to highlight the time-dependent dynamical evolution exhibited by complex cellulosebased materials, not accessible through conventional 1D FTIR-ATR analysis, can provide useful notions for the development and optimization of CNSs based devices for diferent applications, including water remediation, drug-delivery and heterogeneous catalysis
Hydration-driven structural evolution in cross-linked cellulose-based xerogels probed by 2DCOS and PCMW2D correlation spectroscopy applied on SANS data
No full textIn this work, small angle neutron scattering (SANS) data of branched polyethyleneimine (bPEI)/TEMPO-oxidized and ultrasonicated cellulose nanofiber (TOUS-CNF) xerogels, namely cellulose nano-sponges (CNSs), at different hydration level (h) and cross-linker amount, were analyzed through a combined approach involving generalized (2DCOS) and perturbation-correlation moving window (PCMW2D) two-dimensional correlation spectroscopy. The aim was to get novel insights into the sequence of structural changes experienced by the xerogel moieties upon hydration, based on the assessment of the cross-correlations existing at different length scales retrieved by the synchronous (SCMs) and asynchronous (ACMs) 2DCOS and PCMW2D correlation maps calculated upon variation in the chosen perturbation variable. It is worth noting that the application of 2DCOS and PCMW2D on SANS data enabled the identification of structural transitions that are not readily apparent from conventional SANS analysis, highlighting the sensitivity of this method in detecting structural dynamics as well as any minor changes in the polymer arrangement at both low and high spatial scales
Recent advances in photocatalytic Minisci reaction: an ecofriendly functionalization of biologically relevant heteroarenes
No full text“Minisci Reaction”, that is the nucleophilic substitution of protonated heteroaromatic bases by carbon centered radicals under oxidative conditions, probably represents the very first and mostly applied example proving that radical chemistry could be considered a valuable tool in organic synthesis. By showing how charged species could significantly affect the products’ distribution, Minisci and co-workers disclosed the potential of homolytic processes, revealing the key role of polar effects in driving the regioselectivity of the reaction. Over the last 50 years, Minisci Reaction has reached its full consecration, finding application in several organic synthetic routes for a wide range of molecules of pharmaceutical and biological interest.
In the last two decades, the photocatalytic approach for the promotion of this chemo- and regio-selective substitution of heteroarenes has been proposed as a potential eco-friendly alternative to the classical thermal routes. In this context, the sunlight-induced nucleophilic radical addition to protonated heteroaromatic bases catalysed by TiO2-based semiconductors could be considered the genesis of the photocatalytic approach. This protocol, which was successfully applied for the generation of a wide range of radical sources, has been widely analysed in the first edition of this volume. Herein, after re-calling some key aspects of the TiO2-photocatalysis, and our progress in the molecular dynamic studies finalized to the future design of ideal TiO2 crystals, we mainly focus on the recent advances in sun- and visible-light mediated Minisci Reaction, outlining the progress behind the state-of-the-art to promote the regio- and even enantioselective functionalization of heteroaromatic bases under under milder and more benign conditions
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