Separation of polar betalain pigments from cacti fruits of Hylocereus polyrhizus by ion-pair high-speed countercurrent chromatography

Polar betacyanin pigments together with betaxanthins from ripe cactus fruits of Hylocereus polyrhizus (Cactaceae) were fractionated by means of preparative ion-pair high-speed countercurrent chromatography (IP-HSCCC) also using the elution–extrusion (EE) approach for a complete pigment recovery. HSCCC separations were operated in the classical ‘head-to-tail’ mode with an aqueous mobile phase. Different CCC solvent systems were evaluated in respect of influence and effectiveness of fractionation capabilities to separate the occurring pigment profile of H. polyrhizus. For that reason, the additions of two different volatile ion-pair forming perfluorinated carboxylic acids (PFCA) were investigated. For a direct comparison, five samples of Hylocereus pigment extract were run on preparative scale (900 mg) in 1-butanol–acetonitrile–aqueous TFA 0.7% (5:1:6, v/v/v) and the modified systems tert.-butyl methyl ether–1-butanol–acetonitrile–aqueous PFCA (2:2:1:5, v/v/v/v) using 0.7% and 1.0% trifluoroacetic acid (TFA) or heptafluorobutyric acid (HFBA) in the aqueous phase, respectively. The chemical affinity to the organic stationary CCC solvent phases and in consequence the retention of these highly polar betalain pigments was significantly increased by the use of the more lipophilic fluorinated ion-pair reagent HFBA instead of TFA. The HFBA additions separated more effectively the typical cacti pigments phyllocactin and hylocerenin from betanin as well as their iso-forms. Unfortunately, similar K_D ratios and selectivity factors α around 1.0–1.1 in all tested solvent systems proved that the corresponding diastereomers, 15S-type pigments cannot be resolved from the 15R-epimers (iso-forms). Surprisingly, additions of the stronger ion-pair reagent (HFBA) resulted in a partial separation of hylocerenin from phyllocactin which were not resolved in the other solvent systems. The pigments were detected by means of HPLC-DAD and HPLC-electrospray ionization–MS using also authentic reference materials.     

Fluctuation Theory for Markov Random Walks

Two fundamental theorems by Spitzer–Erickson and Kesten–Maller on the fluctuation-type (positive divergence, negative divergence or oscillation) of a real-valued random walk \((S_{n})_{n\ge 0}\) with iid increments \(X_{1},X_{2},\ldots \) and the existence of moments of various related quantities like the first passage into \((x,\infty )\) and the last exit time from \((-\infty ,x]\) for arbitrary \(x\ge 0\) are studied in the Markov-modulated situation when the \(X_{n}\) are governed by a positive recurrent Markov chain \(M=(M_{n})_{n\ge 0}\) on a countable state space \(\mathcal {S}\); thus, for a Markov random walk \((M_{n},S_{n})_{n\ge 0}\). Our approach is based on the natural strategy to draw on the results in the iid case for the embedded ordinary random walks \((S_{\tau _{n}(i)})_{n\ge 0}\), where \(\tau _{1}(i),\tau _{2}(i),\ldots \) denote the successive return times of M to state i, and an analysis of the excursions of the walk between these epochs. However, due to these excursions, generalizations of the aforementioned theorems are surprisingly more complicated and require the introduction of various excursion measures so as to characterize the existence of moments of different quantities.     

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Stereochemistry from X-Ray Diffraction Studies of Three Palladium(II) Complexes with Terdentate Chelating Amines

X-ray crystal structure analysis of three Pd(II) complexes with cis-3,5-diaminopiperidine (DAPI) shows that the metal ion has a square planar coordination. The DAPI groups are trans in the protonated and mixed complexes. Most surprisingly, the unprotonated complex has a basket-like structure with the DAPI groups cis.     

Die Kristallstrukturen von zwei mononuklearen Peroxotitan (IV)-dipicolinaten

The crystal structures of two mononuclear peroxotitanium(IV) chelates, the triclinic, deep red, pleochroitic diaquoperoxotitanium dipicolinate [TiO₂(C₇H₃O₄N) (H₂O)₂]2H₂O, and the monoclinic, orange difluoroperoxotitanium dipicolinate K₂[TiO₂(C₇H₃O₄N)F₂]2H₂O, have been determined from X-ray diffractometer data, and refined to R = 2.7% (3488 reflections) and R = 5.1% (2324 reflections) respectively. Analogous to a yellow-orange dinuclear peroxotitanium dipicolinate described earlier, the utanium atoms are coordinated approximately pentagonal bipyramidally, with the peroxo group and the chelate ligand occupying the equatorial sites and with H₂O or F- forming the apices. The O? O bond length in the peroxo group is the same in all structures, but there is a very slight variation of the Ti-peroxide distances apparently connected with the colours of the compounds. The more basic the apical ligands are (H₂O → F^? → μ-oxygen), the higher is the frequency of the absorption band, the longer are the Ti-peroxide distances, and the shorter are the apical bond lengths. Difference Fourier maps based on the final structures agree with this. The red diaquo complex shows highest residual peaks between titanium and the peroxo group, whereas the orange difluoro complex shows them near the apical Ti? F bonds. The packing of the complexes and hydrogen bonding are discussed. H? O distances seem to indicate that the very acidic diaquo complex is near a transitional state towards a hydroxonium salt.