Clay and charcoal composites: characterisation and application of factorial design analysis for dye adsorption

The characterisation of smectite clay, charcoal and prepared clay-charcoal composites was carried out through the X-ray diffractometry, energy dispersive X-ray spectroscopy (EDS), simultaneous thermal analysis (TGA/DTA), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The analysis revealed the composites to have different characteristics from the precursor clay and charcoal, and a peak displacement (d ₀₀₁) was observed through the X-ray diffraction; this suggests the incorporation of charcoal into the clay lamellas and the formation of a new phase. Tests of adsorption with methylene blue dye were also carried out to evaluate the percentage of dye removal by the adsorbent, in which the composites presented better results than charcoal, indicating great potential for industrial use. A 2³ factorial design was employed to evaluate the influence of temperature, ionic strength and pH on the adsorption of methylene blue using the AV₅₀ composite that presented the best adsorption efficiency.     

Gas phase SMB for propane/propylene separation using enhanced 13X zeolite beads

A gas phase simulated moving bed technology using improved 13X zeolite beads and isobutane as desorbent is assessed for the separation of propane/propylene. Adsorption equilibrium (via gravimetric method) and dynamics (via breakthrough curves) were determined in order to validate the mathematical model used to describe the adsorption process. Simulation results have shown that it is possible to separate propylene from a mixture with propane using gas phase SMB technology. The results indicate that high purity propylene (99.99 % desorbent free basis) can be recovered up to 99.96 % with a productivity of 17.6 mol kg^?1 h^?1, with propane being also recovered at high levels (99.98 %) and high purity (99.89 % desorbent free basis). Comparing the SMB simulation results obtained for this new 13X zeolite beads with those obtained with a commercial 13X zeolite characterized elsewhere, it was found that the productivity of the process was raised by 25 %, with half desorbent consumption.     

Highly enantioselective acylation of chlorohydrins using Amano AK lipase from P. fluorescens immobilized on silk fibroin–alginate spheres

Aromatic, allylic, and aliphatic compounds containing a chlorohydrin group were selected as substrates for the enzymatic kinetic resolution mediated by Amano AK lipase from Pseudomonas fluorescens immobilized in silk friboin-alginate spheres. Thus, the enantioselectivity of the process was sufficient for the production of the desired alcohols and acetates in good yields and high enantiomeric purities. This Letter provides a simple, cheap, and practical protocol for enantioselective synthesis of chlorohydrins and reinforces the versatility of silk fibroin as supports for heterogeneous catalysts.     

(R)-bis-Binaphthoxy iodo lanthanides as catalysts for Diels–Alder reactions

[(R)-1,1′bi-2,2′-Naphthoxy]LnI(THF)₂ (Ln: Yb, Sm, La) 5 have been prepared by reaction of the bispotassium salt of (R)-binaphthol with lanthanide triiodides, and characterized. They are active catalysts for Diels–Alder reactions although with low asymmetric inductions. The lanthanum iodo bisbinaphthoxide gives a slightly higher enantiomeric excess than the two other complexes.     

Comparative binding energy analysis of haloalkane dehalogenase substrates: Modelling of enzyme-substrate complexes by molecular docking and quantum mechanical calculations

We evaluate the applicability of automated molecular docking techniques and quantum mechanical calculations to the construction of a set of structures of enzyme-substrate complexes for use in Comparative binding energy (COMBINE) analysis to obtain 3D structure-activity relationships. The data set studied consists of the complexes of eighteen substrates docked within the active site of haloalkane dehalogenase (DhlA) from Xanthobacter autotrophicus GJ10. The results of the COMBINE analysis are compared with previously reported data obtained for the same dataset from modelled complexes that were based on an experimentally determined structure of the DhlA-dichloroethane complex. The quality of fit and the internal predictive power of the two COMBINE models are comparable, but better external predictions are obtained with the new approach. Both models show a similar composition of the principal components. Small differences in the relative contributions that are assigned to important residues for explaining binding affinity differences can be directly linked to structural differences in the modelled enzyme-substrate complexes: (i) rotation of all substrates in the active site about their longitudinal axis, (ii) repositioning of the ring of epihalohydrines and the halogen substituents of 1,2-dihalopropanes, and (iii) altered conformation of the long-chain molecules (halobutanes and halohexanes). For external validation, both a novel substrate not included in the training series and two different mutant proteins were used. The results obtained can be useful in the future to guide the rational engineering of substrate specificity in DhlA and other related enzymes.     

Synthesis of C3 benzo[1,2-e:3,4-e':5,6-e"]tribenzo[l]acephenanthrylenes ("crushed fullerene" derivatives) by intramolecular palladium-catalyzed arylation

The C60 polyarenes 4, 5, 18 a, and 18 b have been synthesized from truxene by triple alkylation at C5, C10, and C15 followed by a palladium-catalyzed intramolecular arylation. The synthesis of "crushed fullerene" C60H30 (2) is the most efficient reported to date and proceeds in 33% overall yield.     

Suitability of selective pressurized liquid extraction combined with gas chromatography-ion-trap tandem mass spectrometry for the analysis of polybrominated diphenyl ethers

A one-step extraction and clean-up method using pressurized liquid extraction (PLE) (selective PLE) combined with gas chromatography-ion-trap tandem mass spectrometry (GC-ITMS-MS) was evaluated for the analysis of polybrominated diphenyl ethers (from tri- to hepta-PBDEs) at low concentrations in fish and shellfish samples. To this end, the performance of an on-line PLE extraction/clean-up method and of a classical Soxhlet extraction and clean-up method using a multi-layer modified silica column were compared. The two sample treatment methods provided similar results, although an important reduction in the sample treatment time (40 min per sample) was achieved using the selective PLE method. In addition, the suitability of the PLE combined with GC-ITMS-MS method was evaluated by comparing the results obtained in the analysis of fish samples with those obtained by gas chromatography-high resolution mass spectrometry (GC-HRMS). Good agreement between both techniques was obtained with differences between the mean values of less than 16%. The selective PLE method coupled to GC-ITMS-MS produced accurate results for PBDE determination with low limits of detection (1.0-16.8 pg g⁻¹ wet weight) and quantification (3.1-51 pg g⁻¹ wet weight) as well as good precision (RSD < 16%). This method has been applied to the analysis of PBDEs in fish and shellfish samples collected at fish markets in Catalonia (NE Spain).     

Structural and morphological characteristics of (Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)TiO<Subscript>3</Subscript> powders obtained by polymeric precursor method

Pb_1−x Sr _x )TiO₃ powders with different compositions (x = 0, 0.10, 0.50, 0.90 and 1) were synthesized by the polymeric precursor method and heat treated at 800 °C for 2 h under air atmosphere. The thermogravimetric and differential scanning calorimetry analyses were performed in the range from 25 to 800 °C in order to estimate the stages corresponding to the water evaporation, organic decomposition and crystallization of these materials. X-ray diffraction patterns and Rietveld analyses showed that the (Pb_1−x Sr _x )TiO₃ phases with strontium content up to x = 0.1 crystallize in a tetragonal structure. The micrographs obtained by scanning electron microscopy and transmission electron microscopy showed that the powders have agglomerated nature, presenting irregular morphologies and polydisperse particle size distribution. The energy dispersive X-ray spectrometry indicated the presence of pure (Pb_0.50Sr_0.50)TiO₃ phase.     

Energetics of lead(II), cadmium(II) and zinc(II) complexes with amino acids

The molar heat capacity and the standard (p ⁰ = 0.1 MPa) molar enthalpies of formation of the crystalline of bis(glycinate)lead(II), Pb(gly)₂; bis(dl-alaninate)lead(II), Pb(dl-ala)₂; bis(dl-valinate)lead(II), Pb(dl-val)₂; bis(dl-valinate)cadmium(II), Cd(dl-val)₂ and bis(dl-valinate)zinc(II), Zn(dl-val)₂, were determined, at T = 298.15 K, by differential scanning calorimetry, and high precision solution-reaction calorimetry, respectively. The standard molar enthalpies of formation of the complexes in the gaseous state, the mean molar metal–ligand dissociation enthalpies, M(II)–amino acid, \( \langle D_{\text{m}} \rangle \)(M–L), were derived and compared with analogous copper(II)–ligand and nickel(II)–ligand.θθ

M(II)–amino acid	\( \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \)(cr)/kJ mol?1
Bis(glycinate)lead(II), Pb(gly)2	?998.9 ± 1.9
Bis(dl-alaninate)lead(II), Pb(ala)2	?1048.7 ± 1.8
Bis(dl-valinate)lead(II), Pb(val)2	?1166.3 ± 2.5
Bis(dl-valinate)cadmium(II), Cd(val)2	?1243.7 ± 2.7
Bis(dl-valinate)zinc(II), Zn(val)2	?1306.1 ± 2.3

     

Worst case uncertainty estimates for routine instrumental analysis

A methodology for the worst case measurement uncertainty estimation for analytical methods which include an instrumental quantification step, adequate for routine determinations, is presented. Although the methodology presented should be based on a careful evaluation of the analytical method, the resulting daily calculations are very simple. The methodology is based on the estimation of the maximum value for the different sources of uncertainty and requires the definition of limiting values for certain analytical parameters. The simplification of the instrumental quantification uncertainty estimation involves the use of the standard deviation obtained from control charts relating to the concentrations estimated from the calibration curves for control standards at the highest calibration level. Three levels of simplification are suggested, as alternatives to the detailed approach, which can be selected according to the proximity of the sample results to decision limits. These approaches were applied to the determination of pesticide residues in apples (CEN, EN 12393), for which the most simplified approach showed a relative expanded uncertainty of 37.2% for a confidence level of approximately 95%.