1,721,011 research outputs found
Advances and Applications in Deep Eutectic Solvents Technology
No full textThe development of new technologies and chemical applications nowadays cannot ignore their impact on the environment, due to the widespread diffusion of environmental pollution and the relative consequences also on human health. In this context, the development of novel non-harmful and green solvents represents an excellent contribution to the cause because commonly used solvents are generally toxic, highly volatile, and hardly biodegradable.
Deep eutectic solvents (DESs) represent a new class of green organic solvents that possess the characteristics that can adequately address this problem. Synthesised via combination through weak interactions of two or more solid substances and without the use of any other solvent, DESs possess many green properties: bio-availability of their components; easy biodegradation; low or absent toxicity as well as low or absent vapor pressure. Moreover, they are able to perform catalytic tasks as the properties of the components reflect on the properties of the mixtures obtained.
The focus of this Special Issue is the use of DESs as alternatives to commonly used organic solvents in different areas such as chemical transformations; extraction/preconcentration procedures; electrochemistry; fundamental structural research, and various other topics in which these solvents are finding fruitful applications for the transition from academia to industrial use
Carbon-Carbon bond formation in acid deep eutectic solvent: chalcones synthesis via Claisen-Schmidt reaction
No full textOne of the most studied properties of novel organic solvents is represented by their use as media for many chemical reactions. In this field Ionic Liquids (ILs) and more recently Deep Eutectic Solvents (DESs) have been playing significant roles for their smart properties. DESs are increasing their relevance thanks to their low toxicity, and because of their simple and cheap preparation that can be carried out by simply mixing two compounds.
In this work we present the studies of the use of an acid DES obtained from 3-(cyclohexyldimethylammonio)propane-1-sulfonate and (1S)-(+)-10-Camphorsulfonic acid (SB3-Cy / CSA) as reaction media and catalyst for carbon-carbon bond formation reaction via Claisen-Schmidt condensation. This powerful and widely used aldol condensation was performed without the use of any catalysts that are usually needed in this reaction, because of the presence of acid CSA in the DES components. We synthesised sixteen substituted chalcones from benzaldehydes and substituted benzaldehydes in combination with acetophenone and substituted acetophenones as probe reactions.
The advantages of the use of this DES in this relevant reaction are represented by: the green properties of the media and its low toxicity; the absence of harmful acids to catalyse the aldol condensation because of the camphorsulfonic acid composing the DES mixture; the recycling and the re-use of the DES in subsequent reaction cycles; the mild conditions and the excellent conversions and yields observed
Biocidal and inhibitory activity screening of de novo synthesized surfactants against two eukaryotic and two prokaryotic microbial species
No full textThirty-six quaternary ammonium salts, of which 28 structurally different non-commercially available surfactants, were tested to screen their biocidal and inhibitory antimicrobial activity. Their activity was compared to commercially available amphiphiles as well as to non-amphiphilic quaternary ammonium salts. As target of these compounds four microbial species were employed of which two (Saccharomyces cerevisiae and Candida albicans) were important yeast in the food and clinical environment and the other two (Escherichia coli and Listeria innocua) represented the Gram negative and positive bacteria, respec- tively. The surfactants showed the ability to kill the microbial cells in water solution and to variably hamper their growth onto agar medium. The non-amphiphilic compounds (which represent analogues of some surfactants used in this study, since they have the same head group but no hydrophobic portion) had little effect in solution and no effect against the microbial growth on plate. Amphoteric and non- amphoteric zwitterionic surfactants showed reduced biocidal activity. The most active antimicrobial agent was N-tetradecyltropinium bromide (23S) surfactant. The presence of cells did not significantly affect the ability to form micelles, as demonstrated by comparative conductometric measurements
Convenient Esterification of Carboxylic Acids by SN2 Reaction Promoted by a Protic Ionic-Liquid System Formed in Situ in Solvent-Free Conditions
No full textThe reaction of esterification of benzoic acid with benzyl chloride was chosen as a model reaction to study the esterification by SN2 promoted by tertiary amine as deprotonating agent. The use of ionic liquid (IL) 1,3-dimethylimidazolium methanesulfonate [MMIm][OMs] as reaction medium has proven to give quantitative yield of the ester, but interestingly the reaction does occur even in solvent-free conditions, where the acid + the amine form a liquid system (a protic IL) in situ. This last methodology was extended to several carboxylic acids in conditions of atom economy (i.e., without excess of any reagent), giving moderately good yields of esters (54–78%) recovered by weight in pure form
FTIR analysis of the metabolomic stress response induced by N-alkyltropinium bromide surfactants in the yeasts Saccharomyces cerevisiae and Candida albicans
No full textThe activity of surfactants against fungal cells has been studied less than against bacteria, although the medical and industrial importance of the former is of paramount importance. In this paper the surfactant biocidal effect was measured in the yeasts Saccharomyces cerevisiae and Candida albicans with a previously described FTIR bioassay which estimates the stress level as function of the FTIR spectra variation of the cells upon exposition to the chemicals. N-tetradecyltropinium bromide was chosen as stressing agent on the basis of previous preliminary study demonstrating its ability to kill prokaryotic and especially eukaryotic cells at concentration around or over the critical micellar concentration (c.m.c.). Here we show that this surfactant is able to inactivate S. cerevisiae cells at 0.4 mM and C. albicans cells at 0.6 mM after 1 h exposition. FTIR analysis revealed that the surfactant induced metabolomics reactions of S. cerevisiae cells in the regions of amides (W2) and fatty acids (W1). In the same way C. albicans cells showed the maximum stress response in amides (W2) and mixed (W3) regions. Variations of the hydrophobic tail of this surfactant produced a reduced level of cell stress with both the 12C and 16C variants; although these two compounds were more effective in inducing cell mortality in S. cerevisiae but not in C. albicans. In conclusion, this paper has shown that, for this surfactant, the n-alkyl chain must vary between 12C and 16C and that the hydrophilic head size is not as critical as the tail length
Acid-base responsive probes for mercury(II) ions in aqueous solution
No full textA simple ratiometric optical method for mercuric ion sensing has been developed using an ensemble of an indicator, such as 7-hydroxy-4-methylcoumarin (7H4MC) and bromothymol blue (BTB), and a receptor, such as N,N-bis(p-methoxybenzyl)-3,6-dioxaoctane-1,8-diamines (bis-pMDODA) and cryptand [2.2.2] (C222), in aqu- eous solution. The equilibrium between indicator and receptor is perturbed by adding Hg2+ ions (0.8–80 μM), due to the formation of a receptor-metal complex, resulting in a change of the UV/Vis spectra. Both sensitivity and selectivity are explained in terms of association constants between receptor and metal ions and equilibrium constants of the reaction between indicator and receptor. Indicator bromothymol blue has also presented a color variation from light blue to yellow upon coordination of Hg2+ to the receptor, which allows a metal naked-eye detection. The detection limit of the system was found to be about 3 μM and the relative standard deviation for five measurements of 20 μM concentration was 5.6%. BTB/7H4MC arrangement showed a particular selectivity over different interfering cations, suffering only interference from Cu2+ ions for Hg2+ sensing
Advantageous Use of Ionic Liquids for the Synthesis of Pharmaceutically Relevant Quinolones
No full textThe advantageous use of ionic liquids (ILs) as alternatives to common DMF as solvent in the Grohe cycloaracylation for the synthesis of pharmaceutically relevant quinolones is reported. ILs showed in many cases shorter reaction times and higher yields, complete conversions of the reactants and easy work-up procedures compared with DMF. Of the ILs screened, tributylmethylammonium methanesulfonate ([ TBMA][MsO]) was selected as the most suitable for further studies. Interestingle, a wide substrate scope was observed and the IL was recycled by a green process. A further step forward in the use of [TBMA][MsO] for quinolone synthesis was the preparation by a one-pot/three-step procedure of the representative 3-carboxy- 4-quinolone acid 16, which was obtained in high yield in a short time. The greener properties of ILs in comparison with DMF and their non-volatility appoint this method as a potentially efficient and alternative approach to the industrial production of quinolones
Role of anionic micelles in self-assembling of fluorescent acridinium-based chemosensors for the detection of mercury (II) ions
No full textnovel off-on
fluorescent sensing system for Hg2+ ions was prepared through self-assembly, by anionic
surfactant micelles, of different combinations of 10-alkylacridinium perchlorates (as
fluorophores, with a
methyl or an n-octyl chain) and N,N-bis(p-alkyloxybenzyl)-3,6-dioxaoctane-1,8-diamines (as receptors,
with a methyl or an n-dodecyl chain) in water solution. The
fluorescence quenching observed in the
absence of metal ions (“off” state), likely due to a photoinduced electron transfer (PET) mechanism from
diamine to acridinium moiety, has demonstrated that a communication between the binding site and the
signaling unit actually occurs. The addition of Hg2+ resulted in its incorporation in the micelle with the
formation of a receptor-metal complex in competition with the PET process, accordingly the
fluorescence
emission of acridinium was restored (“on” state). The experimental data suggested that compartmentalization
effects in the different micellar microenvironments, due to the different hydrophobic degree of
the components, can affect the
fluorescence response of the sensor and therefore its sensitivity. These
systems showed good sensitivity in Hg2+ sensing and its concentration can be linearly determined
according to the
fluorescence quenching
STRUCTURE EFFECTS OF AMPHIPHILIC AND NON-AMPHIPHILIC QUATERNARY AMMONIUM SALTS ON PHOTODEGRADATION OF ALIZARIN RED-S CATALYZED BY TITANIUM DIOXIDE
No full textThe role of surfactants such as single- and double-tailed tetralkylammonium bromide and various non-amphiphilic tetraalkylammonium salts was investigated on the TiO2 photocatalyzed degradation of 3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt (Alizarin Red-S, ARS) in air-equilibrated alkaline medium under UV light irradiation. Absorption spectral analysis showed that the photodegradation efficiency of the dye was significantly enhanced by the addition of the cationic surfactants. Two interesting findings emerged from this study: ARS was almost completely degraded at surfactant concentration close to 1 mM (value well above the cmc in the experimental conditions); moreover, increasing the surfactant concentration, the photocatalytic reaction became less and less efficient and significantly dependent on the surfactant headgroup size. The presence of a maximum of efficiency depending on the surfactant concentration was due to the combination of catalytic and inhibiting processes. The first one likely depended on the ability of the surfactant to improve the ARS approach to the semiconductor through the formation of cationic bilayers on the TiO2 particles; this effect made the ARS more easily oxidized by TiO2. This catalytic action of the surfactant was opposed by the increasing of the micellar aggregates number in aqueous bulk, which competes with the TiO2 sites in associating to the dye. This was supported by the results obtained with the non-amphiphilic alkylammonium bromide. In this case a higher amount of salt must be added to reach the same maximum efficiency of ARS photooxidation. This is due to the lower capability of neutralization of these salts of both the ARS and the TiO2 surface; the inhibiting effect was not evidenced anymore
- …
