Use of green alternative solvents in dispersive liquid-liquid microextraction: A review

Dispersive liquid-liquid microextraction is one of the most widely used microextraction techniques currently in the analytical chemistry field, mainly due to its simplicity and rapidity. The operational mode of this approach has been constantly changing since its introduction, adapting to new trends and applications. Most of these changes are related to the nature of the solvent employed for the microextraction. From the classical halogenated solvents (e.g., chloroform or dichloromethane), different alternatives have been proposed in order to obtain safer and non-pollutants microextraction applications. In this sense, low-density solvents, such as alkanols, switchable hydrophobicity solvents, and ionic liquids were the first and most popular replacements for halogenated solvents, which provided similar or better results than these classical dispersive liquid-liquid microextraction solvents. However, despite the good performances obtained with low-density solvents and ionic liquids, researchers have continued investigating in order to obtain even greener solvents for dispersive liquid-liquid microextraction. For that reason, in this review, the evolution over the last five years of the three types of solvents already mentioned and two of the most promising solvent alternatives (i.e., deep eutectic solvents and supramolecular solvents), have been studied in detail with the purpose of discussing which one provides the greenest alternative.     

Benzene dilution shifts and steric interactions in N,N-dialkylamides

The NMR spectra of ten disubstituted amides have been recorded at 0°C in carbon tetrachloride and in benzene solutions. The benzene dilution shifts (ASIS) and proton spin decoupling were used to make the chemical shift assignments. A time-averaged solvent cluster model for the association between the amide and benzene is consistent with the observed ASIS values. The assignments for the N-methine and N-methyl resonance peaks in RCON[CH(CH₃)₂]₂, where R is methyl, ethyl or propyl are inverted from the assignments for N,N-diisopropylformamide (R ? H).     

Cobalt‐Catalyzed Cross‐Coupling of 3‐ and 4‐Iodopiperidines with Grignard Reagents

A cobalt‐catalyzed cross‐coupling between 3‐ and 4‐iodopiperidines and Grignard reagents is disclosed. The reaction is an efficient, cheap, chemoselective, and flexible way to functionalize piperidines. This coupling was used as the key step to realize a short synthesis of (±)‐preclamol. Some mechanistic investigations were conducted that highlight the formation of radical intermediates.     

Conformational analysis of N,N-diisopropylamides by combined use of n.m.r. lanthanide-induced shifts and conformational energy calculations

A new method of conformational analysis has been developed, in which energy minimization calculations are combined with lanthanide-induced shift data. First, exhaustive energy calculations are carried out on the free molecules in order to determine the conformations of lowest energy. Then, the coordinates of all low energy conformations or pairs of conformations are used in the pseudocontact shift equation for lanthanide-induced shifts in order to find which of the theoretically obtained conformation(s) gives the best agreement with experiment. The molecules complexed to the lanthanide shift reagent were N,N-diisopropylformamide (DIPF) and N,N-diisopropylacetamide (DIPA). Two different lanthanide shift reagents were used, Eu(fod)₃

1 Fod is the anion of 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione-d₂₇.

and Pr(fod)₃, in order to check the validity of the method. Proton magnetic resonance spectra were taken at 6 °C in carbon tetrachloride solution. The principal conformation found was different for each amide. DIPF was found to exist as a mixture of I (39 mol%) and II (61 mol%) with Eu(fod)₃, and a mixture of I (37%) and II (63%) with Pr(fod)₃. DIPA was found to exist as a mixture of I (79%) and IV (21%) with Eu(fod)₃ and a mixture of I (87%) and IV (13%) with Pr(fod)₃. For both molecules, the two conformations of lowest computed energy were also the pair which gave the best fit to the lanthanide shift reagent data. The location of the principal magnetic axis of the complex was found to lie between 0° and 14° from the lanthanide atom–oxygen atom bond axis. The technique of combining lanthanide shift reagent data with energy calculations shows great promise in conformational analysis.     

Asymmetric synthesis of the (S)-1,1-dioxido-isothiazolidin-3-one phosphotyrosine mimetic via reduction of a homochiral (R)-oxido-isothiazolidin-3-one

[structure: see text]. The first asymmetric synthesis of the (S)-1,1-dioxido-isothiazolidin-3-one ((S)-IZD) pTyr mimetic, which has been incorporated into the recently reported potent protein tyrosine phosphatase 1B (PTP1B) inhibitors, is presented herein. The key reaction is the reduction of the (R)-oxido-isothiazolidin-3-one heterocycle with excellent regiochemical and stereochemical control (>98% ee; 82% yield).     

Scarlet Flax Linum grandiflorum (L.) In Vitro Cultures as a New Source of Antioxidant and Anti-Inflammatory Lignans

In vitro cultures of scarlet flax (Linum grandiflorum L.), an important ornamental flax, have been established as a new possible valuable resource of lignans and neolignans for antioxidant and anti-inflammatory applications. The callogenic potential at different concentrations of α-naphthalene acetic acid (NAA) and thidiazuron (TDZ), alone or in combinations, was evaluated using both L. grandiflorum hypocotyl and cotyledon explants. A higher callus induction frequency was observed on NAA than TDZ, especially for hypocotyl explants, with a maximum frequency (i.e., 95.2%) on 1.0 mg/L of NAA. The presence of NAA (1.0 mg/L) in conjunction with TDZ tended to increase the frequency of callogenesis relative to TDZ alone, but never reached the values observed with NAA alone, thereby indicating the lack of synergy between these two plant growth regulators (PGRs). Similarly, in terms of biomass, NAA was more effective than TDZ, with a maximum accumulation of biomass registered for medium supplemented with 1.0 mg/L of NAA using hypocotyls as initial explants (DW: 13.1 g). However, for biomass, a synergy between the two PGRs was observed, particularly for cotyledon-derived explants and for the lowest concentrations of TDZ. The influence of these two PGRs on callogenesis and biomass is discussed. The HPLC analysis confirmed the presence of lignans (secoisolariciresinol (SECO) and lariciresinol (LARI) and neolignan (dehydrodiconiferyl alcohol [DCA]) naturally accumulated in their glycoside forms. Furthermore, the antioxidant activities performed for both hypocotyl- and cotyledon-derived cultures were also found maximal (DPPH: 89.5%, FRAP 866: µM TEAC, ABTS: 456 µM TEAC) in hypocotyl-derived callus cultures as compared with callus obtained from cotyledon explants. Moreover, the anti-inflammatory activities revealed high inhibition (COX-1: 47.4% and COX-2: 51.1%) for extract of hypocotyl-derived callus cultures at 2.5 mg/L TDZ. The anti-inflammatory action against COX-1 and COX-2 was supported by the IC₅₀ values. This report provides a viable approach for enhanced biomass accumulation and efficient production of (neo)lignans in L. grandiflorum callus cultures.     

Microwave-assisted silica-supported aluminum chloride-catalyzed Friedel-Crafts alkylation

Microwave irradiation is a popular method in organic synthesis to achieve high yields in shorter reaction times. This decreases total ‘man-hours’ in a synthetic setting. Another technique used in organic chemistry to decrease manual manipulations, is solid support reagents. The benefits of this approach is that upon completion of a reaction, a simple filtration can be performed which expedites the work-up and also produces less organic waste. Friedel-Crafts alkylation has been explored using microwave chemistry as well as with solid-supported reagents. In comparison with traditional heating, as well as with AlCl₃, superior yields were observed with silica-gel bound aluminum chloride (Si-AlCl_x) when microwave irradiated for only 5 min.     

Structural diversity and versatility for organoaluminum complexes supported by mono- and di-anionic aminophenolate bidentate ligands

The present contribution describes the synthesis and structural characterization of structurally diverse organoaluminum species supported by variously substituted aminophenolate-type ligands: these Al complexes are all derived from the reaction of AlMe₃ with aminophenols 2-CH₂NH(R)-C₆H₃OH (1a, R = mesityl (Mes); 1b, R = 2,6-di-isopropylphenyl (Diip)) and 2-CH₂NH(R)-4,6-^tBu₂-C₆H₂OH (1c, R = Mes; 1d, R = Diip). The low temperature reaction of AlMe₃ with 1a–b readily affords the corresponding Al dimeric species [μ-η¹,η¹-N,O-{2-CH₂NH(R)-C₆H₄O}]₂Al₂Me₄ (2a–b), consisting of twelve-membered ring aluminacycles with two μ-η¹,η¹-N,O-aminophenolate units, as determined by X-ray crystallographic studies. Heating a toluene solution of 2a (80 °C, 3 h) affords the quantitative and direct formation of the dinuclear aluminium complex Al[η²-N; μ,η²-O-{2-CH₂N(Mes)-C₆H₄O}](AlMe₂) (4a) while species 2b, under the aforementioned conditions, affords the formation of the Al dimeric species [η²-N,O-{2-CH₂N(Dipp)-C₆H₄O}AlMe]₂ (3b), as deduced from X-ray crystallography for both 3b and 4a. In contrast, the reaction of bulky aminophenol pro-ligands 1c–d with AlMe₃ afford the corresponding monomeric Al aminophenolate chelate complexes η²-N,O-{2-CH₂NH(R)-4,6-^tBu₂-C₆H₂O}AlMe₂ (5c–d; R = Mes, Diip; Scheme 3) as confirmed by X-ray crystallographic analysis in the case of 5d. Subsequent heating of species 5c–d yields, via a methane elimination route, the corresponding Al-THF amido species η²-N,O-{2-CH₂N(R)-4,6-^tBu₂-C₆H₂O}Al(Me)(THF) (6c–d; R = Mes, Diip). Compounds 6c–6d, which are of the type {X₂}Al(R)(L) (L labile), may well be useful as novel well-defined Lewis acid species of potential use for various chemical transformations. Overall, the sterics of the aminophenol backbone and, to a lesser extent, the reaction conditions that are used for a given ligand/AlMe₃ set essentially govern the rather diverse “structural” outcome in these reactions, with a preference toward the formation of mononuclear Al species (i.e. species 5c–d and 6c–d) as the steric demand of the chelating N,O-ligand increases.     

Thermoluminescence and optical properties of some dosimetric materials

Thermoluminescence and optical properties of LiF:Mg,Cu,P; BaSO₄:Dy; BaSO₄; Eu and -Al₂O₃:C were investigated as a part of a broader research project on TL mechanisms in various materials. The effects of ionizing radiation on these phosphors are determined in this work by means of thermoluminescence and optical absorption experiments with the aim of identifying new defects formed in these systems and of testing dosimetric characteristics.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Thermoluminescence (TL) of europium-doped ZrO2 obtained by sol–gel method

This article reports the preparation and characterization of europium-doped zirconium oxide (ZrO₂:Eu³⁺) formed by homogeneous precipitation from propoxyde of zirconium [Zr(OC₃H₇)₄]. The alkoxide sol gel process is an efficient method to prepare the zirconium oxide matrix by the hydrolysis of alkoxide precursors followed by condensation to yield a polymeric oxo-bridged ZrO₂ network. All compounds were characterized by thermal analysis and the X-ray diffractometry method. The thermoluminescence (TL) emission properties of ZrO₂:Eu³⁺ under beta radiation effects are studied. The europium-doped sintered zirconia powder presents a TL glow curve with two peaks (Tmax) centered at around 204 and around 292 ^°C, respectively. TL response of ZrO₂:Eu³⁺ as a function of beta-absorbed dose was linear from 2 Gy up to 90 Gy. The europium ion (Eu³⁺)-doped ZrO₂ was found to be more sensitive to beta radiation than undoped ZrO₂ obtained by the same method and presented a little fading of the TL signal compared with undoped zirconium oxide.