The role of ionic liquids in the biocatalytic evaluation of bisphenol levels as contaminant: an automatic approach.

An automatic assay was developed that is intended to be a generic tool for evaluation of a horseradish peroxidase activity in different ionic liquids (ILs). Ionic liquids with different characteristics were used and their effects on the enzymatic reaction, were compared with those obtained with conventional organic solvents. In addition, ILs were tested as solvents for the enzyme substrate (bisphenol A (BPA)). ILs were shown to be a good alternative to conventional organic solvents from either the effect on enzymatic activity or the solubilization of bisphenol. Since bisphenol A is an endocrine disruptor frequently used in plastic industries, it was also applied the developed enzymatic methodology for quantification of this compound in real beverage samples. To increase the sensitivity (already increased by the use of an IL) and the selectivity of the methodology, a sample pre-treatment using a molecular recognition solid phase extraction was applied. Finally, the methodology presented detection and quantification limits of 7.73 × 10-4 and 1.29 × 10-3 mmol L-1 and a linear range up to 1.00 mmol L-1, allowing accurate and reliable quantifications of bisphenol in beer and cola drink samples. This work confirmed the potential of a sequential injection analysis (SIA) system as a simple, versatile, robust, and rapid analytical tool for automating enzymatic assays in ILs medium and, at the same time, showed it to be a relevant automatic alternative for routine determinations of bisphenol A in food samples.

Chiral Derivatives of Xanthones: Investigation of the Effect of Enantioselectivity on Inhibition of Cyclooxygenases (COX-1 and COX-2) and Binding Interaction with Human Serum Albumin.

Searching of new enantiomerically pure chiral derivatives of xanthones (CDXs) with potential pharmacological properties, particularly those with anti-inflammatory activity, has remained an area of interest of our group. Herein, we describe in silico studies and in vitro inhibitory assays of cyclooxygenases (COX-1 and COX-2) for different enantiomeric pairs of CDXs. The evaluation of the inhibitory activities was performed by using the COX Inhibitor Screening Assay Kit. Docking simulations between the small molecules (CDXs; known ligands and decoys) and the enzyme targets were undertaken with AutoDock Vina embedded in PyRx-Virtual Screening Tool software. All the CDXs evaluated exhibited COX-1 and COX-2 inhibition potential as predicted. Considering that the (S)-(-)-enantiomer of the nonsteroidal anti-inflammatory drug ketoprofen preferentially binds to albumin, resulting in lower free plasma concentration than (R)-(+)-enantiomer, protein binding affinity for CDXs was also evaluated by spectrofluorimetry as well as in in silico. For some CDXs enantioselectivity was observed.

Environmental Impact of Ionic Liquids: Recent Advances in (Eco)toxicology and (Bio)degradability.

This Review aims to integrate the most recent and pertinent data available on the (bio)degradability and toxicity of ionic liquids for global and critical analysis and on the conscious use of these compounds on a large scale thereafter. The integrated data will enable focus on the recognition of toxicophores and on the way the community has been dealing with them, with the aim to obtain greener and safer ionic liquids. Also, an update of the most recent biotic and abiotic methods developed to overcome some of these challenging issues will be presented. The review structure aims to present a potential sequence of events that can occur upon discharging ionic liquids into the environment and the potential long-term consequences.

Environmental Impact of Ionic Liquids: Automated Evaluation of the Chemical Oxygen Demand of Photochemically Degraded Compounds.

A novel automated fluorimetric technique was developed for the assessment of the chemical oxygen demand (COD) of ionic liquids (ILs) and combined with a photodegradation step to promote IL degradation. The method was implemented on a sequential injection analysis (SIA) system and is based on the reduction of cerium(IV) in the presence of irradiated ILs. Compounds incorporating the chloride anion were found to exhibit higher COD values and 1-butyl-3-methylimidazolium chloride ([bmim]+ [Cl]- ), 1-butyl-1-methylpyrrolidinium chloride ([bmpyr]+ [Cl]- ), and1-hexyl-3-methylimidazolium chloride ([hmim]+ [Cl]- ) also exhibited considerable photodegradability, whereas the cholinium cation and methanesulfonate and tetrafluoroborate anions showed resistance to photolysis. The developed methodology proved to be a simple, affordable, and robust method, showing good repeatability under the tested conditions (rsd <3.5 %, n=10). Therefore, it is expected that the developed approach can be used as a screening method for the preliminary evaluation of compounds' potential impact in the aquatic field. Additionally, the photolysis step presents an attractive option to promote degradation of ILs prior to their release into wastewater.

Assessment of ionic liquids' toxicity through the inhibition of acylase I activity on a microflow system.

Acylase I (ACY I) plays a role in the detoxication and bioactivation of xenobiotics as well in other physiological functions. In this context, an automated ACY I assay for the evaluation of ionic liquids' (ILs) toxicity was developed. The assay was implemented in a sequential injection analysis (SIA) system and was applied to eight commercially available ILs. The SIA methodology was based on the deacetylation of N-acetyl-l-methionine with production of l-methionine, which was determined using fluorescamine. ACY I inhibition in the presence of ILs was monitored by the decrease of fluorescence intensity. The obtained results confirmed the influence of ILs' structural elements on its toxicity and revealed that pyridinium and phosphonium cations, longer alkyl side chains and tetrafluoroborate anion displayed higher toxic effect on enzyme activity. The developed methodology proved to be robust and exhibited good repeatability (RSD < 1.3%, n = 10), leading also to a reduction of reagents consumption and effluents production. Thus, it is expected that the proposed assay can be used as a novel tool for ILs' toxicity screening.

Automated evaluation of protein binding affinity of anti-inflammatory choline based ionic liquids.

In this work, an automated system for the study of the interaction of drugs with human serum albumin (HSA) was developed. The methodology was based on the quenching of the intrinsic fluorescence of HSA by binding of the drug to one of its binding sites. The fluorescence quenching assay was implemented in a sequential injection analysis (SIA) system and the optimized assay was applied to ionic liquids based on the association of non-steroidal anti-inflammatory drugs with choline (IL-API). In each cycle, 100 µL of HSA and 100 µL of IL-API (variable concentration) were aspirated at a flow rate of 1 mL min(-1) and then sent through the reaction coil to the detector where the fluorescence intensity was measured. In the optimized conditions the effect of increasing concentrations of choline ketoprofenate and choline naproxenate (and respective starting materials: ketoprofen and naproxen) on the intrinsic fluorescence of HSA was studied and the dissociation constants (Kd) were calculated by means of models of drug-protein binding in the equilibrium. The calculated Kd showed that all the compounds bind strongly to HSA (Kd<100 µmol L(-1)) and that the use of the drugs in the IL format does not affect or can even improve their HSA binding. The obtained results were compared with those provided by a conventional batch assay and the relative errors were lower than 4.5%. The developed SIA methodology showed to be robust and exhibited good repeatability in all the assay conditions (rsd<6.5%).

Automated cytochrome c oxidase bioassay developed for ionic liquids' toxicity assessment.

A fully automated cytochrome c oxidase assay resorting to sequential injection analysis (SIA) was developed for the first time and implemented to evaluate potential toxic compounds. The bioassay was validated by evaluation of 15 ionic liquids (ILs) with distinct cationic head groups, alkyl side chains and anions. The assay was based on cytochrome c oxidase activity reduction in presence of tested compounds and quantification of inhibitor concentration required to cause 50% of enzyme activity inhibition (EC50). The obtained results demonstrated that enzyme activity was considerably inhibited by BF4 anion and ILs incorporating non-aromatic pyrrolidinium and tetrabutylphosphonium cation cores. Emim [Ac] and chol [Ac], on contrary, presented the higher EC50 values among the ILs tested. The developed automated SIA methodology is a simple and robust high-throughput screening bioassay and exhibited good repeatability in all the tested conditions (rsd<3.7%, n=10). Therefore, it is expected that due to its simplicity and low cost, the developed approach can be used as alternative to traditional screening assays for evaluation of ILs toxicity and identification of possible toxicophore structures. Additionally, the results presented in this study provide further information about ILs toxicity.

Exploitation of pulsed flows for on-line dispersive liquid-liquid microextraction: Spectrophotometric determination of formaldehyde in milk.

Formaldehyde is often added to foods as a preservative, but it is highly toxic to humans, having been identified as a carcinogenic substance. It has also been used for the adulteration of milk in order to diminish the bacteria count and increase the shelf life of the product. Herein, we present a green dispersive liquid-liquid microextraction procedure in a flow-batch system for the determination of formaldehyde in milk. Pulsed flows were exploited for the first time to improve the dispersion of the extractant in the aqueous phase. The Hantzsch reaction was used for the derivatization of formaldehyde and the product was extracted with the ionic liquid (IL) trihexyltetradecylphosphonium chloride with methanol as the disperser. The flow-batch chamber was made of stainless steel with the facility for resistive heating to speed up the derivatization reaction. Spectrophotometric measurements were directly carried out in the organic phase using an optical fiber spectrophotometer. The limit of detection and coefficient of variation were 100 µg L(-1) and 3.1% (n=10), respectively, with a linear response from 0.5 to 5.0 mg L(-1), described by the equation A=0.088+0.116CF (mg L(-1)) in which A is absorbance and CF is formaldehyde concentration in mg L(-1). The estimated recoveries of formaldehyde from spiked milk samples ranged from 91% to 106% and the slopes of the analytical curves obtained with reference solutions in water or milk were in agreement, thus indicating the absence of matrix effects. Accuracy was demonstrated by the agreement of the results with those achieved by the reference fluorimetric procedure at the 95% confidence level. The proposed procedure allows for 10 extractions per hour, with minimized reagent consumption (120 µL of IL and 3.5 µL acetylacetone) and generation of only 6.7 mL waste per determination, which contribute to the eco-friendliness of the procedure.

Nanoparticle-based assays in automated flow systems: A review.

Nanoparticles (NPs) exhibit a number of distinctive and entrancing properties that explain their ever increasing application in analytical chemistry, mainly as chemosensors, signaling tags, catalysts, analytical signal enhancers, reactive species generators, analyte recognition and scavenging/separation entities. The prospect of associating NPs with automated flow-based analytical is undoubtedly a challenging perspective as it would permit confined, cost-effective and reliable analysis, within a shorter timeframe, while exploiting the features of NPs. This article aims at examining state-of-the-art on continuous flow analysis and microfluidic approaches involving NPs such as noble metals (gold and silver), magnetic materials, carbon, silica or quantum dots. Emphasis is devoted to NP format, main practical achievements and fields of application. In this context, the functionalization of NPs with distinct chemical species and ligands is debated in what concerns the motivations and strengths of developed approaches. The utilization of NPs to improve detector's performance in electrochemical application is out of the scope of this review. The works discussed in this review were published in the period of time comprised between the years 2000 and 2013.

The aquatic impact of ionic liquids on freshwater organisms.

Ionic liquids (ILs), also known as liquid electrolytes, are powerful solvents with a wide variety of academic and industrial applications. Bioassays with aquatic organisms constitute an effective tool for the evaluation of ILs' toxicity, as well as for the prediction and identification of possible moieties that act as toxicophores. In this work, the acute toxicity of six ILs and two commonly used organic solvents was evaluated using freshwater organisms: Daphnia magna, Raphidocelis subcapitata and Hydra attenuata. The bioassays were performed by exposing the organisms to increasing concentrations of the ILs and observing D. magna immobilization, R. subcapitata growth inhibition, and the morphological or mortality effects in H. attenuata. The results demonstrate that the tested organisms are not equally susceptible to the ILs, e.g., bmpyr [BF4] was the least toxic compound for R. subcapitata, N1,1 [N1,1,1OOH] for D. magna and emim [Tf2N] for H. attenuata. This highlights the importance of applying a battery of assays in toxicological analysis. Additionally, Hydra proved to be the most tolerant species to the tested ILs. According to their hazard rankings, the tested ILs are considered practically harmless or moderately toxic, except (Hex)3(TDec)P [Cl], which was classified as highly toxic. The ILs were revealed to be more harmful to aquatic systems than the tested organic solvents, reaffirming the need to analyze carefully the (eco)toxicological impact of these compounds. The present study provides additional data in the evaluation of the potential hazard and the impact of ILs in the environment.

Evaluation of ionic liquids as alternative solvents for aldolase activity: Use of a new automated SIA methodology.

An automated methodology is proposed for the evaluation of a set of ionic liquids (ILs) as alternative reaction media for aldolase based synthetic processes. For that, the effect of traditionally used organic solvents and ILs on the activity of aldolase was studied by means of a novel automated methodology. The implemented methodology is based on the concept of sequential injection analysis (SIA) and relies on the aldolase based cleavage of d-fructose-1,6 diphosphate (DFDP), to produce dihydroxyacetone phosphate (DHAP) and d-glyceraldehyde-3-phosphate (G3P). In the presence of FeCl3, 3-methyl-2-benzothiazoline hydrazine (MBTH) forms a blue cation that can be measured at 670nm, by combination with G3P. The influence of several parameters such as substrate and enzyme concentration, temperature, delay time and MBTH and FeCl3 concentration were studied and the optimum reaction conditions were subsequently selected. The developed methodology showed good precision and a relative standard deviation (rsd) that does not exceed 7% also leading to low reagents consumption as well as effluent production. Resorting to this strategy, the activity of the enzyme was studied in strictly aqueous media and in the presence of dimethylformamide, methanol, bmpyr [Cl], hmim [Cl], bmim [BF4], emim [BF4], emim [Ac], bmim [Cl], emim [TfMs], emim [Ms] and Chol [Ac] up to 50%. The results show that the utilization of ILs as reaction media for aldolase based organic synthesis might present potential advantages over the tested conventional organic solvents. The least toxic IL found in this study was cho [Ac] that causes a reduction of enzyme activity of only 2.7% when used in a concentration of 50%. Generally, it can be concluded that ILs based on choline or short alkyl imidazolium moieties associated with biocompatible anions are the most promising ILs regarding the future inclusion of these solvents in synthetic protocols catalyzed by aldolase.

Immobilization of Distinctly Capped CdTe Quantum Dots onto Porous Aminated Solid Supports.

Immobilization of quantum dots (QDs) onto solid supports could improve their applicability in the development of sensing platforms and solid-phase reactors by allowing the implementation of reusable surfaces and the execution of repetitive procedures. As the reactivity of QDs relies mostly on their surface chemistry, immobilization could also limit the disruption of solution stability that could prevent stable measurements. Herein, distinct strategies to immobilize QDs onto porous aminated supports, such as physical adsorption and the establishment of chemical linking, were evaluated. This work explores the influence of QD capping and size, concentration, pH, and contact time between the support and the QDs. Maximum QD retention was obtained for physical adsorption assays. Freundlich and Langmuir isotherms were used to analyze the equilibrium data. Gibbs free energy, enthalpy, and entropy were calculated and the stability of immobilized QDs was confirmed.

Toxicity assessment of ionic liquids with Vibrio fischeri: an alternative fully automated methodology.

A fully automated Vibrio fischeri methodology based on sequential injection analysis (SIA) has been developed. The methodology was based on the aspiration of 75 µL of bacteria and 50 µL of inhibitor followed by measurement of the luminescence of bacteria. The assays were conducted for contact times of 5, 15, and 30 min, by means of three mixing chambers that ensured adequate mixing conditions. The optimized methodology provided a precise control of the reaction conditions which is an asset for the analysis of a large number of samples. The developed methodology was applied to the evaluation of the impact of a set of ionic liquids (ILs) on V. fischeri and the results were compared with those provided by a conventional assay kit (Biotox(®)). The collected data evidenced the influence of different cation head groups and anion moieties on the toxicity of ILs. Generally, aromatic cations and fluorine-containing anions displayed higher impact on V. fischeri, evidenced by lower EC50. The proposed methodology was validated through statistical analysis which demonstrated a strong positive correlation (P>0.98) between assays. It is expected that the automated methodology can be tested for more classes of compounds and used as alternative to microplate based V. fischeri assay kits.

Improved activity of α-chymotrypsin in mixed micelles of cetyltrimethylammonium bromide (CTAB) and ionic liquids: a kinetic study resorting to sequential injection analysis.

In the present work an automatic methodology, based on sequential injection analysis, (SIA) for the kinetic evaluation of α-chymotrypsin (α-CT) activity in cetyltrimethylammonium bromide (CTAB)/ionic liquid (IL) mixed micelles, was developed. The α-CT-catalysed hydrolysis of N-succinyl-l-phenylalanine-p-nitroanilide (SPpNA) was monitored by following the change in absorbance at 410nm brought about by the formation of p-nitroaniline (pNA). The influence of parameters such as reagents concentration, flow rate, as well as reaction coil length, on the sensitivity and performance of the SIA system were studied and the optimum reaction conditions were subsequently selected. The effect of CTAB/IL micelles on the catalytic constant Kcat and apparent Michaelis-Menten constant (KM) for SPpNA hydrolysis was then studied. The kinetic assays evidence that CTAB/ILs mixed micellar systems can induce α-CT superactivity. In order to perform a critical evaluation of the obtained results, CMC and average micellar size of CTAB/hmim[Cl], CTAB/bmim[Cl], CTAB/bmpyr[Cl] and CTAB/bmpy[Cl] mixed micelles were evaluated by fluorescence and dynamic light scattering, respectively. The SIA methodology showed to be an interesting tool for evaluation of α-CT activity in mixed micelles as it proved to be robust and exhibited good repeatability in all the assay conditions leading also to a reduction of the consumption of solvents as well as of effluent production.

Automated evaluation of pharmaceutically active ionic liquids' (eco)toxicity through the inhibition of human carboxylesterase and Vibrio fischeri.

The toxicity of 16 pharmaceutical active ionic liquids (IL-APIs) was evaluated by automated approaches based on sequential injection analysis (SIA). The implemented bioassays were centered on the inhibition of human carboxylesterase 2 and Vibrio fischeri, in the presence of the tested compounds. The inhibitory effects were quantified by calculating the inhibitor concentration required to cause 50% of inhibition (EC50). The EC50 values demonstrated that the cetylpyridinium group was one of the most toxic cations and that the imidazolium group was the less toxic. The obtained results provide important information about the safety of the studied IL-APIs and their possible use as pharmaceutical drugs. The developed automated SIA methodologies are robust screening bioassays, and can be used as a generic tools to identify the (eco)toxicity of the structural elements of ILs, contributing to a sustainable development of drugs.

Imidazolium ionic liquids as solvents of pharmaceuticals: influence on HSA binding and partition coefficient of nimesulide.

In this work, the influence of imidazolium ionic liquids (ILs) on bio-chemical parameters that influence the in vivo behavior of nimesulide was evaluated. In this context, the binding of nimesulide to human serum albumin (HSA), in IL media, was studied. In parallel, the evaluation of the interaction of drug-IL systems, with micelles of hexadecylphosphocholine (HDPC), enabled the calculation of partition coefficients (K(p)). Both assays were performed in buffered media in the absence and in the presence of emim [BF(4)], emim [Ms] and emim [TfMs] 1%. Even though there was an increase of the dissociation constant (K(d)) in IL media, nimesulide still binds to HSA by means of strong interactions. The thermodynamic analysis indicates that the interaction is spontaneous for all the tested systems. Moreover, the studied systems exhibited properties that are favorable to the interaction of the drug with biological membranes, with K(p) values 2.5-3.5 higher than in aqueous environment. The studied nimesulide-IL systems presented promising characteristics regarding the absorption and distribution of the drug in vivo, so that the studied solvents seem to be good options for drug delivery.

Automated carboxylesterase assay for the evaluation of ionic liquids' human toxicity.

Aiming the prediction of ionic liquids' (ILs) human toxicity, an automated carboxylesterase activity assay was developed. The method was implemented on a sequential injection analysis (SIA) system and relied on the hydrolysis of 4-methylumbelliferyl acetate by the enzyme, to produce the fluorescent compound 4-methylumbelliferone (λ(exc)=365 nm; λ(em)=460 nm). The adopted approach was based on activity/inhibition assays in which the reduction of enzyme activity was denoted by a decrease of fluorescence. The activity assays were performed in aqueous media and in the presence of increasing concentrations of seven commercially available ILs and sodium bis(p-nitrophenyl) phosphate, a strong inhibitor of carboxylesterase. The inhibitory effects were quantified by means of the calculation of half maximal inhibitory effective concentration (EC(50)) values that were between 38 and 134 µmol L(-1). This allowed us to perform some considerations about the toxicity of the compounds. The less and more toxic ILs found in this study were emim [Ms] and tbph [Ms], respectively. The developed SIA methodology is robust and exhibits good repeatability in all the tested conditions (rsd<5.0%, n=10). At the same time a reduction of costs was attained by reduced consumption of reagents and minimal effluent production (2 mL per cycle).

ß-Galactosidase activity in mixed micelles of imidazolium ionic liquids and sodium dodecylsulfate: A sequential injection kinetic study.

An automated methodology for the kinetic study of ß-galactosidase activity in sodium dodecylsulfate (SDS)/ionic liquid (IL) mixed micelles was developed. The main objective of the work was the evaluation of mixed micelles as reaction media for the industrial synthesis of glyco-oligossacharides. Enzyme activity was evaluated by means of a model reaction with the fluorescent substrate 4-methylumbelliferyl-α-d-galactopyranoside (MUG). The assay was implemented in a sequential injection analysis (SIA) system and enzyme activity was studied in SDS/bmim [BF(4)] and SDS/hmim [Cl] mixed micelles with variable concentrations of both components. In order to perform a critical evaluation of the obtained results, CMC and average micellar size of SDS/hmim [Cl] mixed micelles were evaluated by fluorescence and dynamic light scattering, respectively. In the micelle characterization assays it was observed that the CMC of the mixed micelles increased with hmim [Cl] concentration up to 1molL(-1). In the presence of higher IL concentrations there were no evidences of micelle formation. Regarding micellar size, it was maximum for an IL concentration of 0.09molL(-1). The kinetic assays evidenced that SDS/bmim [BF(4)] and SDS/hmim [Cl] mixed micellar systems can led to an increase of enzyme activity. This increase is dependent on the variation of the average micellar size that occurs with the increase of IL concentration up to 0.09molL(-1). It was also noticed that the most promising systems are those incorporating SDS and IL in concentrations under 50mmolL(-1) and 0.5molL(-1), respectively(.) These results evidenced that the studied ILs can modify the physico-chemical properties of the surfactant solution in a favourable way regarding ß-galactosidase activity being an important achievement for the future implementation of industrial processes catalyzed by this enzyme, mainly the synthesis of glyco-oligossacharides. Indeed, surfactant/IL mixed micelles proved to be an interesting alternative to conventional organic solvents in this field enabling the implementation of the processes in a relatively hydrophobic media with enhanced enzyme activity.

Automated high-throughput Vibrio fischeri assay for (eco)toxicity screening: application to ionic liquids.

An automated high-throughput Vibrio fischeri assay was developed and further applied to the evaluation of ionic liquids (ILs) (eco)toxicity. The assay was based on the reduction of bacterial bioluminescence in the presence of test compounds and the results were presented as EC(50). The assays were performed with eight commercially available ILs with distinct cationic head groups, alkyl side chains and anions. EC(50) values between 6.5 and 691.9 mmol L(-1) were obtained for the tested ILs, being hmim [Cl] the most toxic and bmim [Cl] the less toxic ones, confirming the influence of the different structural elements. Moreover, all the tested ILs exhibited a (eco)toxicity lower than Cu(II), used as a positive control during the optimization and analysis steps. The automated assay assured the precise control of the contact time between V. fischeri and test compound by means of a simple protocol that guaranteed adequate aspiration and handling of the solutions as well as the precise implementation of a computer controlled stop period. Furthermore, a significant reduction of the assay costs was achieved through automation mainly by a drastic reduction of the volume of bacterial suspension and test compound. The methodology was validated by comparison with a microplate assay; it was stated that the results, obtained after a 3min contact time, changed proportionally relatively to Cu(II) in both assays. This confirmed the applicability of the methodology as an (eco)toxicity screening assay, with reduction of time and increase of robustness and repeatability (n=10; rsd<1.1%). It is expected that due to its simplicity and reduced cost the developed assay can be integrated in the early stage of development of new compounds as a rapid screening test.

Enzyme based assays in a sequential injection format: a review.

Sequential injection analysis systems have been extensively exploited in the last decades for the implementation of enzyme based assays aiming the evaluation of enzyme activity or the determination of specific analytes. The most prominent aspects of the automation of enzymatic assays in these systems are discussed in this review. Special attention is devoted to the mode of enzyme manipulation in homogeneous or heterogeneous media and to the comparison with batch and flow injection enzyme methodologies. The possibility of implementing strategies for the enhancement of selectivity in specific determinations is also addressed. The more recent trends in this field are discussed focusing mainly on the miniaturization resorting to the lab-on valve platform as well as on the bead injection concept.