The role of accessibility in the characterization of porous solids and their adsorption properties

This paper addresses the role of accessibility for adsorption in porous solids on the adsorption properties including Henry constant, adsorption isotherms and isosteric heat of adsorption. The relevant parameters are the accessible volume, the accessible geometrical surface area and the accessible pore size and its associated volume. This concept will be demonstrated to be important and calls for the need to consider adsorption characteristics in the most coherent and consistent manner. It is particularly reinforced by the limitations inherent in the conventional ways in determining the void volume, surface area and pore size. We provide a number of examples to support this; the challenge that faces us is the development of consistent experimental procedures to determine these accessible quantities. We define the accessible pore size as the size of the largest sphere that rests on three closest solid atoms in such a manner that any probe particle residing in that sphere would have a non-positive solid-fluid potential energy. For each accessible pore size there is an associated accessible pore volume, giving rise to a new accessible pore size distribution (APSD). This is distinct from the classical pore size distribution commonly used in the literature, and in our definition of accessible pore size, a zero pore size is possible. It is also emphasized that the accessible quantities that we introduce here are dependent on the choice of molecular probe, which is entirely consistent with the concept of molecular sieving.     

Dispersive liquid–liquid microextraction combined with nonaqueous capillary electrophoresis for the determination of fluoroquinolone antibiotics in waters

Dispersive liquid–liquid microextraction (DLLME) was combined for the first time with NACE‐UV for the selective determination of eight fluoroquinolone antibiotics (lomefloxacin, levofloxacin, marbofloxacin, ciprofloxacin, sarafloxacin, enrofloxacin, danofloxacin and difloxacin) in mineral and run‐off waters. Field‐enhanced sample injection was carried out in order to improve the sensitivity, whereas pipemidic acid was used as internal standard. The BGE that provided complete separation of the eight analytes and the internal standard was composed of 3 M acetic acid, 49 mM ammonium acetate in 55:45 v/v methanol:ACN. Optimum DLLME conditions (extraction of 5 mL of water at pH 7.6 with 685 μL of CHCl₃ and 1250 μL of ACN, extractant and disperser solvents, respectively) were achieved by means of experimental design methodology. Calibration curves of the whole method were obtained with correlation coefficients (R) higher than 0.994 in all cases. An accuracy and precision study was carried out at different levels of concentration, finding that there were no significant differences (Student's t‐test) between real and spiked concentrations.     

Metabolomics of meat exudate: Its potential to evaluate beef meat conservation and aging

In this study we analyzed the exudate of beef to evaluate its potential as non invasive sampling for nuclear magnetic resonance (NMR) based metabolomic analysis of meat samples. Exudate, as the natural juice from raw meat, is an easy to obtain matrix that it is usually collected in small amounts in commercial meat packages. Although meat exudate could provide complete and homogeneous metabolic information about the whole meat piece, this sample has been poorly studied. Exudates from 48 beef samples of different breeds, cattle and storage times have been studied by ¹H NMR spectroscopy. The liquid exudate spectra were compared with those obtained by High Resolution Magic Angle Spinning (HRMAS) of the original meat pieces. The close correlation found between both spectra (>95% of coincident peaks in both registers; Spearman correlation coefficient = 0.945) lead us to propose the exudate as an excellent alternative analytical matrix with a view to apply meat metabolomics. 60 metabolites could be identified through the analysis of mono and bidimensional exudate spectra, 23 of them for the first time in NMR meat studies. The application of chemometric tools to analyze exudate dataset has revealed significant metabolite variations associated with meat aging. Hence, NMR based metabolomics have made it possible both to classify meat samples according to their storage time through Principal Component Analysis (PCA), and to predict that storage time through Partial Least Squares (PLS) regression.     

Crystal structures and magnetic properties of two octacyanotungstate(IV) and (V)-cobalt(II) three-dimensional bimetallic frameworks

The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [W(IV)[(mu-CN)(4)Co(II)(H(2)O)(2)](2).4H(2)O](n) (1) and [[W(V)(CN)(2)](2)[(mu-CN)(4)Co(II)(H(2)O)(2)](3).4H(2)O](n) (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) A, c = 13.003(2) A, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13.543(5) A, b = 16.054(6) A, c = 15.6301(9) A, and Z = 4. The structure of 1 shows alternating eight-coordinated W(IV) and six-coordinated Co(II) ions bridged by single cyanides in a three-dimensional network. The geometry of each [W(IV)(CN)(8)](4-) entity in 1 is close to a square antiprism. Its eight cyanide groups are coordinated to Co(II) ions which have two coordinated water molecules in trans position. The structure of 2 consists of alternating eight-coordinated W(V) and six-coordinated Co(II) ions linked by single cyanide bridges in a three-dimensional network. Each [W(V)(CN)(8)](3-) unit shows a geometry close to a square antiprism. Only six of its eight cyanide groups are coordinated to Co(II) ions while the other two are terminal. The Co(II) ion in 2 has the same CoN(4)O(2) environment as in 1. The magnetic behavior of 1 is that of magnetically isolated high spin Co(II) ions (S(Co) = 3/2), bridged by the diamagnetic [W(IV)(CN)(8)](3-) units (S(W(IV)) = 0). The magnetic behavior of 2, where the high spin Co(II) ions are bridged by the paramagnetic [W(V)(CN)(8)](3-) units [S(W(V)) = 1/2], is that of ferromagnetically coupled Co(II) and W(V) giving rise to an ordered ferromagnetic phase below 18 K. The magnetic properties of 1 are used as a blank to extract the parameters that are useful to analyze the magnetic data of compound 2.     

1H‐HRMAS NMR study of cold smoked Atlantic salmon (Salmo salar) treated with E‐beam

¹H High resolution magic angle spinning (HRMAS) NMR spectroscopic data in combination with principal components analysis and analysis of variance were used to differentiate between irradiated and non‐irradiated cold‐smoked Atlantic salmon (Salmo salar). NMR profiling was obtained, with a spectral acquisition time of less than 8 min, from a small sample size of intact white salmon muscle, by non‐destructive analysis that includes a very simple and rapid sample preparation step. Results obtained enable the use of creatine, trimethylamine oxide and the sum of phosphorylcholine and glycerophosphorylcholine as diagnostic compounds to detect irradiation treatment. This study shows the potential of ¹H‐HRMAS to be a rapid method for investigating compositional changes due to food processing as well as to confirm the presence or absence of some bioactive compounds in irradiated samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Base‐Dependent Stereodivergent Intramolecular Aza‐Michael Reaction: Asymmetric Synthesis of 1,3‐Disubstituted Isoindolines

The nucleophilic addition (A_N) / intramolecular aza‐Michael reaction (IMAMR) process on Ellman’s tert‐butylsulfinyl imines, bearing a Michael acceptor in the ortho position, is studied. This reaction affords 1,3‐disubstituted isoindolines with a wide range of substituents in good yields and diastereoselectivities. Interestingly, careful choice of the base for the aza‐Michael step allows either the cis or the trans diastereoisomers to be exclusively obtained. This stereodivergent cyclization has enabled the synthesis of C₂‐symmetric bisacetate‐substituted isoindolines. In addition, bisacetate isoindolines bearing two well‐differentiated ester moieties are also noteworthy because they may allow for the orthogonal synthesis of β,β′‐dipeptides using a single nitrogen atom as a linchpin.     

Rechargeable sodium-ion battery based on a cathode of copper hexacyanoferrate

Journal of Solid State Electrochemistry - In this work, the performance of copper (II) hexacyanoferrate(III) (CuHCF) as a cathode material for sodium-ion batteries was studied. The compound was...     

Detailed peak fitting analysis of the Zn 2p photoemission spectrum for metallic films and its initial oxidation stages

The metallic Zn 2p photoemission spectra hold a complex background that requires individual assignment of Shirley background for each peak comprising the spectra. For this reason, a close fit requires the use of the Shirley‐Vegh‐Salvi‐Castle background‐type under the active background approach. We found that the intensity of the plasmon peaks and their associated background cannot be described through existing energy loss (intrinsic and extrinsic) formalisms. We also analyzed the Zn 2p and O 1s spectra for the initial stages of oxide formation at various oxygen exposures. We found that the composition of the oxide layer is ZnO_1.00±0.10 for all exposures, suggesting that our assessment of the primary function of metallic Zn is accurate and can be employed for quantitative studies. We also present a set of parameters to accurately fit and resolve the metallic and oxide Zn 2p peaks.