A micellar electrokinetic chromatography approach using diastereomeric derivatization and a volatile surfactant for the enantioselective separation of selenomethionine

A MEKC methodology with UV detection was developed for the enantioselective separation of selenomethionine (SeMet). The use of (+)‐1‐(9‐fluorenyl)ethyl chloroformate (FLEC) as chiral derivatization reagent to form SeMet diastereomers enabled their subsequent separation using ammonium perfluorooctanoate (APFO) as a volatile pseudostationary phase. The effect of APFO concentration and pH, temperature, injection volume, and derivatization conditions (time and FLEC/SeMet ratio) were evaluated in order to select the best separation conditions. A chiral resolution of 4.4 for DL‐SeMet was achieved in less than 6 min using 100 mM APFO at pH 8.5 as electrophoretic buffer. Satisfactory results were obtained in terms of linearity, precision (RSD from 3.4 to 5.1% for migration times and from 1.8 to 4.6% for corrected peak areas), accuracy, and LODs (3.1 × 10^?6 M and 3.7 × 10^?6 M for d and l enantiomers, respectively). The method was successfully applied to the determination of l ‐SeMet in food supplements.     

The characterization of electronic defect states of single and double carbon vacancies in graphene sheets using molecular density functional theory

ABSTRACT

A detailed picture of the electronic states manifolds of single- and double-vacancy defects in molecular models of graphene based on polycyclic aromatic hydrocarbons (PAHs) is presented. DFT calculations using various density functionals including long-range corrected ones have been performed for pyrene, circumpyrene and 7a,7z-periacene. It has been found for pyrene defect models that DFT results reproduced well the set of closely-spaced singlet and triplet states predicted by the CCSD(T) and previous MRCI?+?Q calculations, indicating the applicability of DFT for accessing the excited states manifolds also for larger graphene models. For the single-carbon vacancy defect, all structures have a triplet ground state. As expected, in the largest system, 7a,7z-periacene-1C, the lowest lying states are much closer in energy. For all double-vacancy defect structures, a significant rearrangement of the electronic states with increasing size of the sheet is observed. The closed-shell ¹A_g state in the smallest systems is destabilised in the extended 7a,7z-periacene system, which has the ³B_2u state as the ground state. As observed for the single-vacancy defect, the lowest lying states are closer in energy for the larger systems, since there are more π orbitals close in energy available. For all states, the formation of the bridging bonds for the double vacancy leads to distances shorter than for the single vacancy defect indicating a larger rigidity of the former structure which does not allow stronger distortions.     

Anti-inflammatory/infection PLA nanoparticles labeled with technetium 99m for in vivo imaging

Despite advancements in treatment of infectious diseases, opportunistic pathogens continue to pose a worldwide threat. Identifying a source of infection/inflammation is often challenging which highlights the need of improved diagnostic agents. Using a model of local S. aureus infection, here we evaluated the potential of betamethasone or dexamethasone loaded in poly (lactic acid) nanoparticles and radiolabeled with 99mTc to detect an infection/inflammation site in vivo. A betamethasone and dexamethasone nanoparticles (NPs) with 200 and 220 nm in size, respectively, were created with a 98% 99mTc radiolabeling efficiency. When injected in infected mice, betamethasone NPs presented a higher accumulation in the infected hind paw in comparison with dexamethasone NPs. Our results suggest that this nanosystem may be a valid nanoradiopharmaceutical for the detection of inflammation/infection foci in vivo.

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Graphical abstract Nanoradiopharmaceutical for inflammation

     

Molecule-based room-temperature magnets: catalytic role of V(III) in the synthesis of vanadium-chromium Prussian blue analogues

A new synthetic procedure to obtain vanadium-chromium Prussian blue analogues is presented, using controlled amounts of V(III) in solution during the synthesis. The vanadium and chromium oxidation states and the chemical environment of the metal ions in the solids are characterized by infrared and X-ray absorption spectroscopies. The presence of weak amounts of V(III) during the synthesis provides materials which are better organized and present reproducible Curie temperature and magnetization at saturation in agreement with the observed V/Cr stoichiometry.     

Structural and photophysical properties of heterobimetallic 4f-zn iminophenolate cryptates

Lanthanide complexes with the Schiff base axial macrobicyclic ligand L(1) react with Zn(II) nitrate in the presence of CaH(2) to yield Ln(III)-Zn(II) heterodinuclear cryptates with the formula [Ln(NO(3))(L(1)-3H)Zn](NO(3)).xH(2)O.yMeOH. The macrobicyclic receptor L(1) is an azacryptand N[(CH(2))(2)N=CH-R-CH=N-(CH(2))(2)](3)N (R = 1,3-(2-OH-5-Me-C(6)H(2))). The crystal structures of the Pr(III), Yb(III), and Lu(III) complexes, chemical formulas [Ln(NO(3))(L(1)-3H)Zn](NO(3)).xSolv (monoclinic, C2/c, Z = 8), as well as that of [Zn(2)(L(1)-3H)](NO(3)).H(2)O (15) (triclinic, P(-)1, Z = 2), have been determined by X-ray crystallography. The ligand is helically wrapped around the two metal ions, leading to pseudo-C(3) symmetries around the metals. The Ln(III)-Zn(II) distances lie in the range 3.3252(13) to 3.2699(14) A, while the Zn(II)-Zn(II) distance in 15 amounts to 3.1037(18) A. The three five-membered chelate rings of the ligand backbone coordinating the Ln(III) ion adopt a (lambdalambdadelta)(5) (or (deltadeltalambda)(5)) conformation while the three pseudochelate rings formed by the coordination of the ligand to the Zn(II) ion adopt a (lambda'lambda'lambda')(5) (or (delta'delta'delta')(5)) conformation. Thus in the solid state the conformation of the three cations is Lambda(deltadeltalambda)(5)(delta'delta'delta')(5) or its enantiomeric form Delta(lambdalambdadelta)(5)(lambda'lambda'lambda')(5). In solution, the helicates present a time-averaged C(3) symmetry, as shown by (1)H NMR, and the conformation of the cations is described as Lambda(deltadeltadelta)(5)(delta'delta'delta')(5) (or Delta(lambdalambdalambda)(5)(lambda'lambda'lambda')(5)). The photophysical properties of the cryptates depend on the nature of the Ln(III) ion, and (L-3H)(3)(-) is revealed to be a good sensitizer for Eu(III) and Tb(III) at low temperatures, but the emission at room temperature is limited by the low energy of the ligand (3)pipi state. While Eu(III) is most effectively sensitized by the ligand triplet state, the Tb(III) ((5)D(4)) sensitization occurs via the singlet state. The quantum yield of the metal-centered luminescence in the Eu-Zn cryptate amounts to 1.05% upon ligand excitation. The low energy of the ligand (3)pipi state allows efficient sensitization of the Nd(III) and Yb(III) cryptates, which emit in the near-infrared.     

A warning on the use of radical traps as a test for radical mechanisms: they react with palladium hydrido complexes

Typical radical traps (galvinoxyl, TEMPO, DPPH) react with palladium hydrides, sometimes at rates competitive with those of palladium hydride catalyzed reactions that follow an insertion mechanism (for example, alkene isomerization). Thus, positive results for radical reaction tests can be misleading. The complexes with more polarizable (neutral complexes rather than cationic) and more accessible hydrides, and the less sterically protected radical traps, react faster.     

Apparent equilibration time required for surfactant-oil-water systems to emulsify into the morphology imposed by the formulation. Part 2: Effect of sec-butanol concentration and initial location

Winsor type I equilibrated surfactant-oil-water (SOW) systems produce o/w emulsions upon stirring. However, if the surfactant is initially dissolved in the oil phase, the attained type after inmediate emulsification is usually w/o. If the SOW system is partially equilibrated, it could result in a normal o/w emulsion, as if it were fully equilibrated. The minimum contact time for that to happen, the so-called apparent equilibration time tAPE, was previously shown (Langmuir 2002, 18, 607) to strongly depend on formulation, surfactant molecular weight, and oil viscosity. The present report shows that it depends on alcohol concentration and location in the unequilibrated system.     

Unusually strong optical interactions between particles in quasi-one-dimensional geometries

A theoretical analysis of the optically induced interaction between small particles in a quasi-one-dimensional system is presented. The total reflection of light modes near a geometric resonance leads to strong radiation pressure on a single particle. The presence of the two particles splits the resonance leading to a nontrivial oscillating interaction. The existence of stable, optically bound dimers under two counterpropagating (noncorrelated) light modes is also discussed.     

Divisorial Elements in Lattice-Ordered Monoids

Let S be a commutative lattice-ordered monoid that is conditionally complete and admits residuals. Imitating the definition of divisorial ideals in commutative ring theory, we study divisorial elements in S. The archimedean divisorial elements behave especially nicely. We establish a Galois correspondence of the divisorial elements in a finite interval. Assuming the maximum condition on integral divisorial elements, it is shown that their Krull associated primes are divisorial and the integral divisorial elements admit irredundant representations as intersections of finitely many p-components that are p-primal divisorial elements.