A Spectroscopic Study of Colchicine in the Solid State and in Solution by Multinuclear Magnetic Resonance and Vibrational Circular Dichroism

Although almost 200‐years‐old, several unknown aspects remain to be explored of colchicine, the unique available drug for acute flares of gout. In this article, we report density‐functional theory (DFT) studies of geometry, energy, and NMR; ¹H‐, ¹³C‐, and ¹⁵N‐NMR chemical shifts and some spin‐spin coupling constants, including the complete analysis of the saturated part (ring B); the assignment of both enantiomers by NMR using a chiral solvating agent; solid‐state NMR experiments of the different forms of natural and racemic colchicine, and IR and vibrational circular dichroism (VCD) studies of these same forms.     

London Dispersion and Hydrogen-Bonding Interactions in Bulky Molecules: The Case of Diadamantyl Ether Complexes

Diadamantyl ether (DAE, C₂₀H₃₀O) represents a good model to study the interplay between London dispersion and hydrogen-bond interactions. By using broadband rotational spectroscopy, an accurate experimental structure of the diadamantyl ether monomer is obtained and its aggregates with water and a variety of aliphatic alcohols of increasing size are analyzed. In the monomer, C−H⋅⋅⋅H−C London dispersion attractions between the two adamantyl subunits further stabilize its structure. Water and the alcohol partners bind to diadamantyl ether through hydrogen bonding and non-covalent O_{water/alcohol}⋅⋅⋅H−C_DAE and C−H_alcohol⋅⋅⋅H−C_DAE interactions. Electrostatic contributions drive the stabilization of all the complexes, whereas London dispersion interactions become more pronounced with increasing size of the alcohol. Complexes with dominant dispersion contributions are significantly higher in energy and were not observed in the experiment. The results presented herein shed light on the first steps of microsolvation and aggregation of molecular complexes with London dispersion energy donor (DED) groups and the kind of interactions that control them.     

4‐Amino‐6‐benzyl­oxy‐2‐(methyl­sulfanyl)‐5‐nitro­so­pyrimidine: hydrogen‐bonded dimers linked into π‐stacked chains

The title compound, C₁₂H₁₂N₄O₂S, crystallizes with Z′ = 2 in space group P2₁/c. The intramolecular dimensions are consis­tent with a highly polarized electronic structure. Each of the independent mol­ecules forms a centrosymmetric dimer linked by paired N—H?N hydrogen bonds, and these dimers are linked into a single type of chain by aromatic π–π‐stacking interactions.     

On-line coupling of automatic solid-phase extraction and HPLC for determination of carotenoids in serum

The automated method developed for the determination of carotenoids uses 200 μL of serum, which was mixed with 400 μL of tetrahydrofuran, vortexed for 1 min, settled for 10 min, centrifuged for 6 min and the supernatant injected into an automatic solid-phase extraction (SPE) system for cleanup-preconcentration. A 10% water-acetonitrile mobile phase at 1.5 mL min⁻¹ eluted the retained compounds and transferred them on-line to a reversed-phase analytical column for individual separation of the target analytes. Visible detection was performed at 450 and 460 nm. The detection limits for the target analytes were between 3 and 30 ng mL⁻¹; the precision (expressed as relative standard deviation) ranged between 2.83 and 5.06% for repeatability and between 3.80 and 7.40% for within laboratory reproducibility. The total analysis time was 18 min. The proposed method is reliable, robust, and has an excellent potential for high-throughput use in both clinical and research laboratories.     

A global optimization algorithm for linear fractional and bilinear programs

In this paper a deterministic method is proposed for the global optimization of mathematical programs that involve the sum of linear fractional and/or bilinear terms. Linear and nonlinear convex estimator functions are developed for the linear fractional and bilinear terms. Conditions under which these functions are nonredundant are established. It is shown that additional estimators can be obtained through projections of the feasible region that can also be incorporated in a convex nonlinear underestimator problem for predicting lower bounds for the global optimum. The proposed algorithm consists of a spatial branch and bound search for which several branching rules are discussed. Illustrative examples and computational results are presented to demonstrate the efficiency of the proposed algorithm.     

A level-density-dependent imaginary potential for heavy ions

Under the assumption that compound-nucleus formation is the only channel competing with elastic scattering, an L-dependent imaginary potential is defined with the help of the compound-nucleus level density. For the latter an expression is used which seems to be accurate enough for excitation energies of several tens of MeV and with a substantial part of rotational energy. Associated with a double-folded real part, this imaginary potential is shown to reproduce well the elastic scattering data of eight systems of medium size (total mass between 36 and 72) at various energies not very high above the Coulomb barrier. The results are equivalent to those obtained with a folding real potential and a Woods-Saxon imaginary potential with parameters adjusted for each set of data with the advantage that our approach only needs two parameters to fit the data for a wide range of energies for each scattering system.     

The expansion of physical quantities in terms of the irreducible representations of the scale-euclidean group and applications to the construction of scale-invariant correlation functions

The irreducible representations of the scale-Euclidean group in three dimensions are introduced, and the general tensor is expanded in terms of these representations. The cases of zero-rank tensor (scalar), rank-1 tensor (vector), and rank-2 tensor are studied in detail. The expansion is shown to be a generalization of the Helmholtz expansion of a vector into rotational and irrotational parts.As in Part I of this work (Concepts: One-Dimensional Problems), the correlations that are introduced are invariant under changes of frames of reference. Correlations are set up between tensors of different ranks and dimensions. A correlation that measures a degree of isotropy is defined.     

Understanding the Aldo‐Enediolate Tautomerism of Glycolaldehyde in Basic Aqueous Solutions

The biochemically important interconversion process between aldoses and ketoses is assumed to take place via 1,2‐enediol or 1,2‐enediolate intermediates, but such intermediates have never been isolated. The current work was undertaken in an attempt to detect the presence of the 1,2‐enediol structure of glycolaldehyde in alkaline medium, actually a 1,2‐enediolate, and to try to clarify the scarce data existing about both the formation of deprotonated enediol and the aldo‐enediolate equilibrium. The Raman spectra of neutral and basic solutions were recorded as a function of time for eleven days. Several bands associated with the presence of the enediolate were observed in alkaline medium. Glycolaldehyde exists as three different structures in aqueous solution at neutral pH, that is, hydrated aldehydes, aldehydes and dimers, with a respective ratio of approximately 4:0.25:1. Additionally, the formation of Z‐enediolate forms takes place at basic pH, together with an increase in the concentration of aldehyde species, such as 2‐oxoethan‐1‐olate, and a decrease in the concentrations of the hydrated aldehyde and dimeric forms. The theoretical ratio of ≈1.5:1 for aldehyde:Z‐enediolate reproduces the experimental Raman spectrum in basic medium, with an additional contribution of the previously mentioned ratio between the hydrated aldehyde and dimeric forms. Finally, Raman spectroscopy allowed us to monitor the enolization of this carbohydrate model and conclude that aldo‐enediol tautomerism—formally aldo‐enediolate—happens when a suitable amount of basic species is added.     

Interface double-exchange ferromagnetism in the Mn-Zn-O system: new class of biphase magnetism

In this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn(3+) and Mn(4+) via a double-exchange mechanism. The presence of the ZnO around MnO(2) modifies the kinetics of MnO(2)-->Mn(2)O(3) reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples.