Folate content in sea buckthorn berries and related products (Hippophaë rhamnoides L. ssp. rhamnoides): LC-MS/MS determination of folate vitamer stability influenced by processing and storage assessed by stable isotope dilution assay

A stable isotope dilution assay was adopted for quantitation of folate vitamers in sea buckthorn berries, juice, and concentrate using fourfold labeled folate isotopologues of the folate derivatives as the internal standards and reversed-phase liquid chromatography-tandem mass spectrometry with electrospray ionization (LC-ESI-MS/MS). Processing effects and storage stability were investigated during juice and concentrate production from sea buckthorn berries (Hippopha? rhamnoides). The technological processing of the berries caused a total degradation of tetrahydrofolate and 5-formyltetrahydrofolate in the generated juice. The content of the main folate vitamer 5-methyltetrahydrofolate remained approximately unchanged during the whole processing from the berries to the concentrate. Sea buckthorn juice was stored under two household storage conditions (6 degrees C, 25 degrees C), and also under accelerated aging conditions (40 degrees C) for up to 7 days to determine the effects of storage temperature on the stability of 5-methyltetrahydrofolate. The content of 5-methyltetrahydrofolate was nearly unchanged during the storage at 6 degrees C after 7 days. The juice showed almost identical degradation of 5-methyltetrahydrofolate of about 17-20% at 25 degrees C and 40 degrees C after 7 days of storage. [figure: see text]     

Lantern-type dinickel complexes: An exploration of possibilities for nickel–nickel bonding with bridging bidentate ligands

Many binuclear nickel complexes have Ni Ni distances suggesting Ni Ni covalent bonds, including lantern-type complexes with bridging bidentate ligands. This DFT study treats tetragonal, trigonal, and digonal lantern-type complexes with the formamidinate, guanidinate, and formate ligands, besides some others. Formal bond orders (ranging from zero to two) are assigned to all the Ni Ni bonds on the basis of MO occupancy considerations. A VB-based electron counting approach assigns plausible resonance structures to the dinickel cores. Model tetragonal complexes with the dimethylformamidinate and the dithioformate ligands have singlet ground states whose non-covalently bonded Ni Ni distances are close to those in their experimentally known counterparts. Trigonal dinickel complexes are unknown, but are predicted to have quartet ground states with Ni Ni bonds of order 0.5. The model digonal complexes are predicted to have triplet ground states, but the predicted Ni Ni bond lengths are longer than those found in their experimentally known counterparts. This could owe to inadequate treatment of electron correlation by DFT in these short Ni Ni bonds with their multiconfigurational character. All the Ni Ni bond distances here are categorized into ranges according to the Ni Ni bond orders of 0, 0.5, 1, 1.5, and 2, no Ni Ni bonds of order higher than two being identified. The Ni Ni bonds of given order in these lantern-type complexes are consistently shorter than the corresponding Ni Ni bonds in dinickel complexes having carbonyl ligands, attributable to the metal metal bond lengthening effect of CO ligands.     

Surface properties of a series of amphiphilic dendrimers with short hydrophobic chains

A series of tree-shaped, amphiphilic dendrimers was synthesized. The products belong to the family of one-directional arborols of the form ([9]-n), where the notation signifies that each molecule has nine hydroxyl groups ([9]-) as the hydrophilic head and an alkyl chain as the hydrophobic moiety (n = 6, 8, or 10 carbon atoms). The surfactant character changes dramatically as the number of methylene groups increases. The critical micelle concentration of [9]-6 was determined, and pressure-area isotherms of the less soluble [9]-8 and [9]-10 were obtained. Large structures existed atop the spread layers. Large structures were also found in solutions of [9]-6.     

The unusual reaction of semiquinone radicals with molecular oxygen

Hydroquinones (benzene-1,4-diols) are naturally occurring chain-breaking antioxidants, whose reactions with peroxyl radicals yield 1,4-semiquinone radicals. Unlike the 1,2-semiquinone radicals derived from catechols (benzene-1,2-diols), the 1,4-semiquinone radicals do not always trap another peroxyl radical, and instead the stoichiometric factor of hydroquinones varies widely between 0 and 2 as a function of ring-substitution and reaction conditions. This variable antioxidant behavior has been attributed to the competing reaction of the 1,4-semiquinone radical with molecular oxygen. Herein we report the results of experiments and theoretical calculations focused on understanding this key reaction. Our experiments, which include detailed kinetic and mechanistic investigations by laser flash photolysis and inhibited autoxidation studies, and our theoretical calculations, which include detailed studies of the reactions of both 1,4-semiquinones and 1,2-semiquinones with O2, provide many important insights. They show that the reaction of O2 with 2,5-di-tert-butyl-1,4-semiquinone radical (used as model compound) has a rate constant of 2.4 +/- 0.9 x 10(5) M-1 s-1 in acetonitrile and as high as 2.0 +/- 0.9 x 10(6) M-1 s-1 in chlorobenzene, i.e., similar to that previously reported in water at pH approximately 7. These results, considered alongside our theoretical calculations, suggest that the reaction occurs by an unusual hydrogen atom abstraction mechanism, taking place in a two-step process consisting first of addition of O2 to the semiquinone radical and second an intramolecular H-atom transfer concerted with elimination of hydroperoxyl to yield the quinone. This reaction appears to be much more facile for 1,4-semiquinones than for their 1,2-isomers.     

A simple Cu-catalyzed coupling approach to substituted 3-pyridinol and 5-pyrimidinol antioxidants

A convenient approach to 3-pyridinols and 5-pyrimidinols via a two-step Cu-catalyzed benzyloxylation/catalytic hydrogenation sequence is presented. The corresponding 3-pyridinamines and 5-pyrimidinamines can be prepared in an analogous sequence utilizing benzylamine in lieu of benzyl alcohol. The radical-scavenging ability of these derivatives are preliminarily explored and reveal that the increased acidities of the pyridinols and pyrimidinols render them susceptible to more significant kinetic solvent effects when compared to phenols.     

Selective determination of acidic pharmaceuticals in wastewater using molecularly imprinted solid-phase extraction

The determination of acidic pharmaceuticals, such as non-steroidal anti-inflammatory drugs NSAIDs and clofibric acid (metabolite of clofibrate), at low ng L⁻¹ levels in wastewater requires highly selective and sensitive analytical procedures. The removal of matrix components during sample preparation results in significant benefits towards reducing the matrix effects during LC-MS analysis. Therefore this work describes a simple method to enrich and clean up NSAIDs and clofibric acid from sewage water using molecularly imprinted solid-phase extraction (MISPE). Final analysis was performed by liquid chromatography-tandem mass spectrometry. The performance of this method has been evaluated in fortified tap and sewage water in terms of recovery, precision, linearity, and method quantification limit. Recovery for all compounds ranged in all matrices between 84 and 116% with intra-day R.S.D. values below 11.5%. Matrix effect evaluation demonstrated that even complex sample matrixes, such as pond or sewage water did not showed significant ion suppression/enhancement compared to tap water. The performance of the method was further emphasized by the study of pond water, which receives treated water from a sewage treatment plant in south Sweden. Raw sewage and treated water were also tested. In those samples, all acidic pharmaceuticals were detected in concentration above method quantification limits ranging from 5.1 to 5153.0 ng L⁻¹.     

Molecular structures of the digermanes Me2XGeGeXMe2 (X = Me, Cl, and H): an ab initio study combined with experimental investigation by Raman spectroscopy and gas electron diffraction

Ab initio calculations were carried out to investigate the potential-energy surface for internal rotation of the methylated digermanes hexamethyldigermane Me(3)GeGeMe(3) ( 1), dichlorotetramethyldigermane Me(2)ClGeGeClMe(2) ( 2), and tetramethyldigermane Me(2)HGeGeHMe(2) ( 3). Different basis sets [6-31+G(d), SDD, aug-cc-pVTZ] were employed at the DFT and MP2 levels of theory to optimize structures and to calculate energies and vibrational frequencies. For 1, one minimum representing a staggered structure was located on the potential-energy surface. For 2 and 3, antiperiplanar conformations with C 2 symmetry were found to be the global minima. Additionally, synclinal minima were located for 2 and 3 when certain basis sets were employed. Determination of structural parameters in the gas phase by gas electron diffraction confirmed the computed predictions for all three compounds. For 2 and 3, the ratios of antiperiplanar to synclinal conformer were detected to be 90:10 (328 K) and 72:28 (293 K), respectively, by gas electron diffraction. The experimentally determined GeGe bond lengths in 1, 2, and 3 in the gas phase are 241.4(1), 242.7(2) (averaged for antiperiplanar and synclinal), and 241.7(1) pm (equal for antiperiplanar and synclinal). Only averaged structures were observed, using Raman spectroscopy, for 2 and 3 because the wavenumber differences are small between conformers and there is only a small contribution from the second conformer in each case. For 2, the crystal structure was also determined by X-ray diffraction. An anticlinal structure (with Cl atoms eclipsing the C atoms) was found with a GeGe bond length of 242.1 pm.     

The phonon spectrum of phase-I ammonia: reassignment of lattice mode symmetries from combined molecular and lattice dynamics calculations

The zone-center phonon spectra of phase-I ammonia and deuterated ammonia have been obtained from plane-wave DFT molecular dynamics and localized basis set harmonic lattice dynamics simulations. These data have proved to be excellent for benchmarking the two approaches. Significant changes to the assignments of the experimental low-frequency lattice modes are proposed on the basis of the calculated data. The magnitude of the splitting of the longitudinal and transverse optical modes has been determined and is shown to be significant in some cases. The high-frequency internal mode region of the spectrum has also been obtained and is shown to be in excellent agreement with the results of previous studies. The symmetry coordinates and Davydov splittings of the internal modes are fully analyzed.     

Catalytic enantioselective thioester aldol reactions that are compatible with protic functional groups

This communication reports highly enantioselective and diastereoselective methyl malonic acid half thioester (MeMAHT) aldol reactions that are compatible with protic functional groups and enolizable aldehydes, affording syn S-phenyl thiopropionates.