Monolithic metal–organic framework MIL‐53(Al)‐polymethacrylate composite column for the reversed‐phase capillary liquid chromatography separation of small aromatics

A monolithic capillary column containing a composite of metal–organic framework MIL‐53(Al) incorporated into hexyl methacrylate‐co‐ethylene dimethacrylate was prepared to enhance the separation of mixtures of small aromatic compounds by using capillary liquid chromatography. The addition of 10 mg/mL MIL‐53(Al) microparticles increased the micropore content in the monolithic matrix and increased the Brunauer–Emmett–Teller surface area from 26.92 to 85.12 m²/g. The presence of 1,4‐benzenedicarboxylate moieties within the structure of MIL‐53(Al) as an organic linker greatly influenced the separation of aromatic mixtures through π–π interactions. High‐resolution separation was obtained for a series of alkylbenzenes (with resolution factors in the range 0.96–1.75) in less than 8 min, with 14 710 plates/m efficiency for propylbenzene, using a binary polar mobile phase of water/acetonitrile in isocratic mode. A reversed‐phase separation mechanism was indicated by the increased retention factor and resolution as the water percentage in the mobile phase increased. A stability study on the composite column showed excellent mechanical stability under various conditions. The higher resolution and faster separation observed at increased temperature indicated an exothermic separation, whereas the negative values for the free energy change of transfer indicated a spontaneous process.     

Preparation and chromatographic properties of a multimodal chiral stationary phase based on phenyl-carbamate-propyl-beta-CD for HPLC

A phenylcarbamate derivative of 2-hydroxypropyl-beta-CD bonded stationary phase was prepared by a previously described method. Its enantiomeric recognition abilities were evaluated as chiral stationary phase (CSP) in normal, polar organic and RP conditions by HPLC. The relevant structural features of the prepared stationary phase which make it an effective chiral selector are discussed. This material seems to have an excellent enantioselectivity for a variety of racemic analytes in the three modes. Hence it can be considered a highly effective multimodal column. Retention factor (k), selectivity (alpha) and resolution (R(s)) were the chosen parameters to describe the column performance. Optimization of these separations was discussed in terms of mobile phase composition, flow rate and structural patterns of the injected analytes.     

Sensitive analysis of amino acids with carrier-mediated single drop microextraction in-line coupled with capillary electrophoresis

In order to analyze amino acids sensitively without derivatization, we have developed carrier-mediated single drop microextraction (SDME). Nonane-1-sulfonic acid was added to an acidic sample donor solution as a carrier to form neutral ion pair complexes with amino acids. The ion pair complexes were extracted to the organic phase, covering a drop of an aqueous basic acceptor phase hanging at the tip of a capillary, and then back-extracted to the basic acceptor phase, where both the amino acids and the carrier have negative charges and the ion pair complexes are broken. The resulting extract of enriched amino acids was injected into the capillary and analyzed by capillary electrophoresis. With 20-min SDME with agitation of the donor phase, enrichment factors of four aromatic amino acids were up to 120-fold, yielding the LOD of 70-500 nM. The linear dynamic ranges for corrected peak areas were 1-100 μM with linear correlation coefficients larger than 0.9959. With internal standardization, the intraday RSDs of migration times and corrected peak areas were 0.01-0.04% and 2.0-3.7%, respectively. The capabilities of sample cleanup including desalting and preconcentration of carrier-mediated SDME were demonstrated with the analysis of human urine after minimal pretreatment of acidification and centrifugation.     

Determination of capsaicinoids in Capsicum species using ultra performance liquid chromatography‐mass spectrometry

In the present work, a rapid and sensitive ultra performance liquid chromatography‐mass spectrometry method has been proposed for the analysis of capsaicinoids (nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin) present in different Capsicum samples. Extraction of capsaicinoids was carried out by liquid–liquid extraction using ethanol as an extracting solvent, while the chromatographic separation was achieved by reversed phase C₁₈ column with gradient mobile phase (solvent A: acetonitrile and solvent B: water with 0.1% formic acid). Under the optimum experimental conditions, the linear ranges were 0.5–50 μg/g with correlation coefficient (r²) >0.999 for each capsaicinoids and detection limits were 0.15, 0.05, 0.06, 0.2, and 0.1 μg/g for nordihydrocapsaicin, capsaicin, dihydrocapsaicin, homocapsaicin, and homodihydrocapsaicin, respectively. Run‐to‐run and day‐to‐day precisions of the method with relative standard deviations <1.5% were achieved for all analyzed capsaicinoids. The robustness of the method was determined by utilizing different injection volumes of the extracts. Furthermore, to validate the system robustness, a run of high number of capsaicinoids present in different varieties of Capsicum samples was performed in this study. All the capsaicinoids were separated in a time of less than 9 min by employing the proposed method.     

A Chemometric Analysis of Compounds from Native New Zealand Medicinal Flora

Several hundred (396) compounds from New Zealand flora with medicinal properties were analyzed for their physicochemical properties. It was found that approximately 10 % fulfilled all the requirements to be considered to be lead‐like, over half of the compounds were deemed to be in the drug‐like space and ≈75 % were in the known drug space. These results indicate the presence of a significant proportion of compounds that are of particular interest to pursue as potential lead compounds or therapeutics. Additionally, compound classes were analyzed separately—most carbonyl‐containing compounds (aldehydes, ketones, esters and lactones), along with phenols were the most lead‐like compounds, which also displayed very good proportions in the drug‐like and known drug space. The information presented herein can be harnessed and utilized in future work, through focussing on the compounds and compound classes that exhibit high‐levels of lead‐likeness for further development.     

Turbulent jet impinging a cylindrical hot cavity

The possibility of improving the heat transfer is investigated numerically using finite volume method. The Reynolds number increase has a minor effect on flow structure but generates a systematic rise of Nusselt Number. The maximum heat exchange occurs when the cavity bottom is located at the potential core end. The main heat exchange occurs on the cavity bottom for every case. The stagnation Nusselt number is correlated according some problem parameters.     

A re-investigation of resveratrol synthesis by Perkins reaction. Application to the synthesis of aryl cinnamic acids

A re-investigation of resveratrol synthesis by Perkins reaction allowed to improve this method and to determine the configuration of the intermediates. The results were applied to the synthesis of several aryl cinnamic acids for biological evaluation.     

A Comparative Analytical Study of Two New Liquid Crystals Used as Stationary Phases in GC

The investigation of the analytical properties of two new nematic sulphur-containing liquid crystals 5-(4-methoxyphenyl)-azophenyl)-2-butylthio-1,3,4-oxadiazole (Phase I) and 5-(4-(propoxyphenyl)-azophenyl)-2-butyl thio-1,3,4-oxadiazole (Phase II) and which comprise units of 1,3,4-oxadiazole instead of the aromatic cycles, was carried out by gas chromatography using glass capillary columns. For this purpose, many solutes belonging to various families and having different polarities and volatilities were injected. Comparison of the retention data of the studied components has shown that Phase II allowed a better separation than the other phase. The two liquid crystalline materials show a good separation of the studied isomers except for xylene.     

Rolling Against a Sphere: The Non-transitive Case

We study the control system of a Riemannian manifold M of dimension n rolling on the sphere \(S^n\). The controllability of this system is described in terms of the holonomy of a vector bundle connection which, we prove, is isomorphic to the Riemannian holonomy group of the cone C(M) of M. Using Berger’s list, we reduce the possible holonomies to a few families. In particular, we focus on the cases where the holonomy is the unitary and the symplectic group. In the first case, using the rolling formalism, we construct explicitly a Sasakian structure on M; and in the second case, we construct a 3-Sasakian structure on M.