Liquid mixtures of xenon with fluorinated species: xenon + sulfur hexafluoride

The vapor-liquid equilibrium of binary mixtures of xenon + SF6 has been measured at nine temperatures from 235.34 to 295.79 K and pressures up to 6.5 MPa. The mixture critical line is found to be continuous between the critical points of the pure components, and hence, the system can be classified as type I phase behavior in the scheme of van Konynenburg and Scott. The excess Gibbs free energies have been calculated, and the experimental results have been interpreted using the statistical associating fluid theory for potentials of variable range (SAFT-VR). Additionally, the SAFT-VR equation has been used to model other systems involving SF6 and alkanes, illustrating the predictability of the approach and further demonstrating the transferability of parameters between binary mixtures involving alkanes and xenon.     

Bioaccumulation assessment of the sunscreen agent 2-ethylhexyl 4-(N,N-dimethylamino)benzoate in human semen by automated online SPE-LC-MS/MS

The proven endocrine disruption nature of the sunscreen ingredient 2-ethylhexyl 4-(N,N-dimethylamino)benzoate (EDP) calls for research to understand its distribution and bioaccumulation in the human body. A sensitive analytical method to determine EDP and its metabolites in human semen based on online SPE-LC-MS/MS is described. The method has been fully validated and a standard addition calibration has been used for quantification to correct the observed matrix effects. The on-column detection limits of the analytes are between 0.2 and 0.6 ng, depending on the analyte and the sample. The repeatability of the method, expressed as relative standard deviation, was in the range 4.6–9.4%. The method was satisfactorily applied to semen samples from male volunteers who were subjected to single and repeated whole-body applications of an EDP-containing sunscreen product. EDP metabolites were found at different concentrations in semen samples from the repeated application study, thus showing evidences of bioaccumulation in humans.     

Targeting metabolomics analysis of the sunscreen agent 2-ethylhexyl 4-(N,N-dimethylamino)benzoate in human urine by automated on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry with liquid chromatography-time-of-flight/mass spectrometry confirmation

The in vivo metabolism of the xenobiotic agent 2-ethylhexyl 4-(N,N-dimethylamino)benzoate (EDP), a UV filter commonly used in sunscreen cosmetic products, was studied by targeting metabolomics analysis in human urine. The metabolomic study involved the use of urine from male and female volunteers before and after application of an EDP-containing sunscreen cosmetic. The metabolism of EDP in urine was studied by using the triple quadrupole detector in a combination of Precursor Ion Scanning and Neutral Loss Scanning modes, with and without enzymatic hydrolysis. Detected metabolites were subsequently confirmed as glucuronide conjugates of 4-(N,N-dimethylamino)benzoic acid and 4-(N-methylamino)benzoic acid by liquid chromatography-time-of-flight/mass spectrometry (LC-TOF/MS) in the accurate mass mode. In this way, the existence of phase II metabolism in the detoxification of EDP by effects of the lipophilic character of this sunscreen agent was confirmed. Hence, to study the in vivo metabolism of EDP, a fully automated method using a solid-phase extraction (SPE) workstation connected on-line to a liquid chromatograph and a triple quadrupole mass analyzer (LC-MS/MS) was developed. The ensuing hyphenated method is very simple and requires minimal human intervention. Following thorough optimization of the SPE and LC-MS/MS conditions, the analytical procedure was validated and standard addition calibration used for the quantitative correction of matrix effects. The proposed method was applied to determine the phase I metabolites of EDP in urine samples and afforded limits of detection from 0.1 to 1.1 ng and accuracy of 91-107% with relative standard deviations in the range 1.5-8.7% (sample volume: 100 μL). Based on the results of in vivo percutaneous absorption of a single application of the sunscreen, about 0.5% of the amount of the applied EDP is excreted in urine.     

Enzymatic regioselective production of chloramphenicol esters

An enzymatic study has been performed in the search for synthetic routes to produce chloramphenicol derivatives through regioselective processes using lipases. Complementary transesterification and hydrolytic reactions have been carried to synthesize chloramphenicol regioisomers. Reaction parameters, such as biocatalyst, solvent, acyl donor, and temperature have been optimised in order to obtain chloramphenicol esters with high yields through acylation processes. Scale-up of the enzymatic reactions (1 g-scale at 0.25 M) and catalyst recycling (up to 10 cycles) have been successfully achieved. Furthermore, monoacylated derivatives at the more hindered secondary position could also be obtained employing hydrolysis processes.     

Cernumidine and isocernumidine, new type of cyclic guanidine alkaloids from Solanum cernuum

Cernumidine and isocernumidine were identified in the ethanol extract of the leaves of Solanum cernuum Vell. together with four known phenolic compounds. The alkaloids have a natural (2-aminopyrrolidin-1-yl)carboxamidine alkaloidal base acylated with isoferulic (3-hydroxy-4-methoxycinnamic) acid with Z and E configurations, respectively. The structures were elucidated on the basis of 1D- and 2D-NMR data and the structure of cernumidine was confirmed by X-ray analysis. Cernumidine displayed inhibition of interleukin-8 production by HT-29 colon carcinoma cells. This fact could orient further research in gastric cancer prevention and treatment.     

Influence of poly(N‐isopropylacrylamide) and poly(N,N′‐diethyl acrylamide) coatings on polysulfone/polyacrylonitrile‐based membranes for protein separation

Herein we describe the design and the assembly of temperature sensitive polysulfone (PS)/polyacrylonitrile (PAN) blend membranes using supercritical fluid technology. Blended membranes were prepared using the CO₂‐assisted phase inversion method, and their pores were coated with two thermoresponsive hydrogels‐poly(N‐isopropylacrylamide) (PNIPAAm) and poly(N,N′‐diethylacrylamide) (PDEAAm). Permeation experiments of bovine serum albumin (BSA) and lysozyme (LYS) solutions were used to evaluate the performance and temperature‐responsive behavior of coated membranes. While membranes coated with PNIPAAm presented similar protein permeation profiles at temperatures below and above its lower critical solution temperature, PDEAAm coating imparted a temperature‐responsive behavior to PS/PAN (90:10) membranes and selective permeation of proteins with different sizes. Copyright © 2011 John Wiley & Sons, Ltd.     

Near‐infrared spectroscopy and partial least squares‐class modeling (PLS‐CM) for metabolomics fingerprinting discrimination of intervention breakfasts ingested by obese individuals

Near‐infrared spectroscopy has been used in nutritional metabolomics fingerprinting for the assessment of the intake of intervention breakfasts prepared with four different vegetable oils that were previously subjected to a deep frying process of 20 cycles for 5 min at 180°C. The target oils were an extra virgin olive oil and three varieties of refined sunflower oil. Of the three latter, one of them was used as such, other was spiked with a synthetic oxidation inhibitor (dimethylsiloxane) and, finally, the last one was enriched with an extract of phenolic compounds from olive pomace, the antioxidant properties of which are well known. Urine sampled from individuals before intake and 2 and 4 h after intake was directly analyzed by NIRS to obtain fingerprint characteristics of the metabolome composition. The resulting urinary patterns were combined for statistical analysis by unsupervised and supervised approaches. Partial least squares‐class modeling enabled to develop class‐models for each intervention breakfast, thus achieving discrimination of urinary fingerprints from individuals after breakfast intake. The models were statistically characterized by estimation of sensitivity and specificity parameters for the training and evaluation (validation) steps. The application of variable importance in projection algorithm enabled to detect the spectral regions with higher significance to explain the variability observed in the partial least squares class‐models. Quantitative differences of variable importance in projection scores discriminated among the different classes under study. Copyright © 2013 John Wiley & Sons, Ltd.     

CUDA parallel programming for simulation of epidemiological models based on individuals

Mathematical models are of great value in epidemiology to help understand the dynamics of the various infectious diseases, as well as in the conception of effective control strategies. The classical approach is to use differential equations to describe, in a quantitative manner, the spread of diseases within a particular population. An alternative approach is to represent each individual in the population as a string or vector of characteristic data and simulate the contagion and recovery processes by computational means. This type of model, referred in the literature as MBI (models based on individuals), has the advantage of being flexible as the characteristics of each individual can be quite complex, involving, for instance, age, sex, pre‐existing health conditions, environmental factors, social habits, etc. However, when it comes to simulations involving large populations, MBI may require a large computational effort in terms of memory storage and processing time. In order to cope with the problem of heavy computational effort, this paper proposes a parallel implementation of MBI using a graphics processor unit compatible with CUDA. It was found that, even in the case of a simple susceptible–infected–recovered model, the computational gains in terms of processing time are significant. Copyright © 2015 John Wiley & Sons, Ltd.     

Asymmetric chemoenzymatic synthesis of N-acetyl-α-amino esters based on lipase-catalyzed kinetic resolutions through interesterification reactions

Several phenylalanine analogs have been synthesized through a four-step route starting from easily available ethyl acetamidocyanoacetate. In a first reaction, and making use of phase transfer catalysts, this compound reacted with several alkyl halides, being benzyltributylammonium chloride identified as the best one for the production of a series of quaternary amino acids in moderate to excellent yields (52–95%). Then, the corresponding N-acetyl-phenylalanine methyl and allyl ester derivatives were obtained through acidic hydrolysis, esterification, and N-acetylation. Rhizomucor miehei lipase was found as a versatile enzyme for the resolution of these amino esters, finding the best results through interesterification reactions with butyl butyrate in acetonitrile. A great influence in the stereoselectivity was found depending on the chemical structure of the compound, achieving for the non- or para-substituted in the phenyl ring excellent stereoselectivities, being moderate for the meta-nitro derivative, while the ortho-nitro amino ester did not react.