Investigation of free and conjugated seleno‐amino acids in wheat bran by hydrophilic interaction liquid chromatography with tandem mass spectrometry

An analytical method for determining seleno‐methionine, methyl‐seleno‐cysteine, and seleno‐cystine in wheat bran was developed and validated. Four different extraction procedures were evaluated to simultaneously extract endogenous free and conjugated seleno‐amino acids in wheat bran in order to select the best extraction protocol in terms of seleno amino acid quantitation. The extracted samples were subjected to a clean‐up by a reversed phase/strong cation exchange solid‐phase extraction and analyzed by chiral hydrophilic interaction liquid chromatography‐tandem mass spectrometry. The optimized extraction protocol was employed to validate the methodology. Process efficiency ranged from 58 to 112% and trueness from 73 to 98%. Limit of detection and limit of quantification were lower than 1 ng/g. Four wheat bran samples were analyzed for both total Se and single seleno‐amino acids determination. The results showed that Se‐ seleno‐methyl‐l selenocysteine was the major seleno‐amino acid in wheat bran while seleno‐methionine and seleno‐cysteine were both minor species.     

Unprecedented Diastereoselective Arylogous Michael Addition of Unactivated Phthalides

The first highly enantioselective arylogous Michael reaction (AMR) of 3-unsubstituted phthalides has been described. This phase-transfer methodology, which uses catalytic amounts of KOH/18-crown-6 catalyst in mesitylene in the presence of N,O-bis(trimethylsilyl)acetamide (BSA), gives access to a broad range of 3-monosubstituted phthalides with high levels of syn diastereoselectivity and good yields, starting from 3-unsubstituted derivatives and diverse α,β-unsaturated carbonyl compounds. The reaction also applies to unactivated 3-alkyl phthalides to afford 3,3-dialkyl derivatives. A plausible mechanism has been suggested. DFT analysis of possible transition states gives a rationale of the high syn diastereoselectivity observed and its correlation with the solvent's dielectric constant.     

Curved domain walls dynamics driven by magnetic field and electric current in hard ferromagnets

The propagation of curved domain walls in hard ferromagnetic materials is studied by applying a reductive perturbation method to the generalized Landau–Lifshitz–Gilbert equation. The extended model herein considered explicitly takes into account the effects of a spin-polarized current as well as those arising from a nonlinear dissipation.     

Polycarbide nickel clusters containing interstitial Ni(eta2-C2)4 and Ni2(micro-eta2-C2)4 acetylide moieties: mimicking the supersaturated Ni-C solutions preceding the catalytic growth of CNTs with the structures of [HNi25(C2)4(CO)32]3- and [Ni22(C2)4(CO)28Cl]3-

Reaction of [Ni(6)(CO)(12)](2-) with CCl(4) in CH(2)Cl(2) gives the [HNi(25)(C(2))(4)(CO)(32)](3-) and [Ni(22)(C(2))(4)(CO)(28)Cl](3-) carbonyl clusters containing interstitial Ni(eta(2)-C(2))(4) and Ni(2)(micro-eta(2)-C(2))(4) acetylide moieties.     

Enhancement of the photocatalytic activity of TiO2 through spatial structuring and particle size control: from subnanometric to submillimetric length scale

This review summarizes the physical approaches towards enhancement of the photocatalytic activity of titanium dioxide by controlling this semiconductor in a certain length scale from subnanometric to submillimetric distances and provides examples in which the photocatalytic activity of TiO2 is not promoted by doping or changes in the chemical composition, but rather by application of physical concepts and spatial structuring of the semiconductor. Thus, encapsulation inside the micropores and cavities of zeolites (about 1 nm) renders small titanium oxide clusters with harnessed photocatalytic activity. On the other hand, nanometric titanium particles can be ordered forming structured periodic mesoporous materials with high specific surface area and well defined porosity. Titiania nanotubes of micrometric length, either independent or forming a membrane, also exhibit unique photocatalytic activity as consequence of the long diffusion length of charge carriers along the nanotube axis. Finally, photonic crystals with an inverse opal structure and the even more powerful concept of photonic sponges can serve to slow down visible light photons inside the material, increasing the effective optical path in such a way that light absorption near the absorption onset of the material is enhanced considerably. All these physical-based approaches have shown their potential in enhancing the photocatalytic activity of titania, paving the way for a new generation of novel structured photocatalysts in which physical and chemical concepts are combined.     

Water droplets as template for next-generation self-assembled poly-(etheretherketone) with cardo membranes

Next generation PEEK-WC membranes have been fabricated by using an innovative self-assembly technique. Patterned architectures have been achieved via a solvent-reduced and water-assisted process, resulting in honeycomb packed geometry. The membranes exhibit monodisperse pores with size and shape comparable to those left by templating water droplets. Influencing factors for the formation of self-assembled poly-(etheretherketone) with Cardo [PEEK-WC] membranes have been evaluated, identifying the critical parameters for nucleation, growth, and propagation of the droplet-mobile arrays through the overall films. Structure-transport relationships have been discussed according to the results achieved from the implementation of membrane distillation processes, yielding indication about the suitability of self-assembled PEEK-WC films to work as interfaces in contactor operations.     

Sn-centred icosahedral Rh carbonyl clusters: synthesis and structural characterization and 13C-{103Rh} HMQC NMR studies

The reaction of [Rh(7)(CO)(16)](3-) with SnCl(2).2H(2)O in a 1 : 1 molar ratio under N(2) results in the formation of the new heterometallic cluster, [Rh(12)Sn(CO)(27)](4-), in very high yield (ca. 86%). Further controlled additions of SnCl(2).2H(2)O, or solutions of HCl, or [RhCl(COD)](2), give [Rh(12)(micro-Cl)(2)Sn(CO)(23)](4-). Similarly, addition of HBr to [Rh(12)Sn(CO)(27)](4-) gives the related cluster [Rh(12)(micro-Br)(2)Sn(CO)(23)](4-). Notably, if the addition of SnCl(2).2H(2)O to [Rh(12)Sn(CO)(27)](4-) is carried out under a CO atmosphere, the reaction takes a different course and leads to the formation of the new cluster, [Rh(12)Sn(micro(3)-RhCl)(CO)(27)](4-). All the above clusters have been shown by single-crystal X-ray diffraction studies to have a metal framework based on an icosahedron, which is centred by the unique Sn atom. Their chemical reactivity and (13)C-{(103)Rh} HMQC NMR spectroscopic characterization are also reported.     

Approximate values for force constant and wave number associated with a low-frequency concerted motion in proteins can be evaluated by a comparison of X-ray structures

Low-frequency internal motions in protein molecules play a key role in biological functions. A direct relationship between low-frequency motions and enzymatic activity has been suggested for bovine pancreatic ribonuclease (RNase A). The flexibility-function relationship in this enzyme has been attributed to a subtle and concerted breathing motion of the beta-sheet regions occurring upon substrate binding and release. Here, we calculate an approximate value for the force constant and the wave number of the low-frequency beta-sheet breathing motion of RNase A, by using the Boltzmann hypothesis on a set of data derived from a simple conventional structural superimposition of an unusual large number of X-ray structures available for the protein. The results agree with previous observations and with theoretical predictions on the basis of normal-mode analysis. To the best of our knowledge, this is the first example in which the wave number and the force constant of a low-frequency concerted motion in a protein are directly derived from X-ray structures.     

A practical synthesis of alpha-aryl methyl ketones via a transition-metal-free Meerwein arylation

We report herein a simple, scalable, transition-metal-free approach to the synthesis of alpha-aryl methyl ketones from diazonium tetrafluoroborate salts under mild conditions. This methodology uses easily accessible and nontoxic starting material and was applied to the multi-kilogram-scale preparation of 1-(3-bromo-4-methylphenyl)propan-2-one.     

Synthesis and X-ray structure of the [{Fe3(CO)9(micro3-O)}2H]3- trianion: dimerization of a metal carbonyl cluster via formation of an exceptionally short hydrogen bond

The synthesis, structure and characterization of the [{Fe3(CO)9(micro3-O)}2H]3- trianion in its [Cs(THF)0.33]+ and [NEt4]+ salt are reported. The title dimeric cluster has been obtained by protonation in water or in organic solvent of the [Fe3(CO)9(micro3-O)]2- dianion to the hydroxo [Fe3(CO)9(micro3-OH)]- derivative and crystallization. The solid state structure of [Cs(THF)0.33]3[{Fe3(CO)9(micro3-O)}2H] is based on ionic packing of [Cs(THF)0.33]+ cations and [{Fe3(CO)9(micro3-O)}2H]3- trianions. The fractional formula is due to the particular packing of Cs+ cations, which are at the vertices of fused cuboctahedral and trigonal antiprismatic polyhedrons. Each cuboctahedron encapsulates a [{Fe3(CO)9(micro3-O)}2H]3- trianion, whereas each trigonal antiprism encapsulates a THF molecule. The possibility that the structure of the [{Fe3(CO)9(micro3-O)}2H]3- trianion could be affected by its confinement in the cuboctahedral cage of Cs+ ions and the heavy disorder of the THF molecule urged a further structural determination of the trianion with a completely different cation. The corresponding [NEt4]3[{Fe3(CO)9(micro3-O)}2H] salt has been, therefore, prepared and structurally characterized. The [{Fe3(CO)9(micro3-O)}2H]3- trianion displays an identical structure and almost coincident molecular parameters in both salts. Its most notable feature is represented by the unique hydrogen atom symmetrically bridging the micro3-O atoms of two different [Fe3(CO)9(micro3-O)]2- molecules and displaying one of shortest O...H...O interaction so far reported in organic, inorganic and organometallic literature. The structure of [Cs(THF)]2[Fe4(CO)13], which has been obtained as a by-product of the synthesis of [Cs(THF)0.33]3[{Fe3(CO)9(micro3-O)}2H], is also briefly reported.