Two isomorphous ZnII/CoII complexes with tri‐tert‐butoxysilanethiol and histamine,and (4‐hydroxymethyl‐1H‐imidazole‐κN)bis(tri‐tert‐butoxysilanethiolato‐κ2O,S)zinc(II)

The complexes [2‐(1H‐imidazol‐4‐yl‐κN³)ethylamine‐κN]bis(tri‐tert‐butoxysilanethiolato‐κS)cobalt(II), [Co(C₁₂H₂₇O₃SSi)₂(C₅H₉N₃)], and [2‐(1H‐imidazol‐4‐yl‐κN³)ethylamine‐κN]bis(tri‐tert‐butoxysilanethiolato‐κS)zinc(II), [Zn(C₁₂H₂₇O₃SSi)₂(C₅H₉N₃)], are isomorphous. The central Zn^II/Co^II ions are surrounded by two S atoms from the tri‐tert‐butoxysilanethiolate ligand and by two N atoms from the chelating histamine ligand in a distorted tetrahedral geometry, with two intramolecular N—H...O hydrogen‐bonding interactions between the histamine NH₂ groups and tert‐butoxy O atoms. Molecules of the complexes are joined into dimers via two intermolecular bifurcated N—H...(S,O) hydrogen bonds. The Zn^II atom in [(1H‐imidazol‐4‐yl‐κN³)methanol]bis(tri‐tert‐butoxysilanethiolato‐κ²O,S)zinc(II), [Zn(C₁₂H₂₇O₃SSi)₂(C₄H₆N₂O)], is five‐coordinated by two O and two S atoms from the O,S‐chelating silanethiolate ligand and by one N atom from (1H‐imidazol‐4‐yl)methanol; the hydroxy group forms an intramolecular hydrogen bond with sulfur. Molecules of this complex pack as zigzag chains linked by N—H...O hydrogen bonds. These structures provide reference details for cysteine‐ and histidine‐ligated metal centers in proteins.     

Determination of selenocysteine and selenomethionine in edible animal tissues by 2D size-exclusion reversed-phase HPLC-ICP MS following carbamidomethylation and proteolytic extraction

A method was developed for the simultaneous determination of selenomethionine (SeMet) and selenocysteine (SeCys) in meat (chicken and lamb muscles) and different offal tissues (heart, liver, kidney). The analytical procedure was based on the protein extraction with urea under reducing conditions (dithiothreitol), derivatization of SeCys and SeMet by carbamidomethylation with iodoacetamide (IAM) followed by quantitative proteolysis. The mixture of the derivatized Se-amino acids was purified by size-exclusion liquid chromatography (LC) and analysed by ion-paring reversed-phase HPLC–inductively coupled plasma mass spectroscopy (ICP MS). The quantification of SeCys and SeMet was carried out by the method of standard additions. ⁷⁷SeMet was used to control the SeMet derivatization efficiency and recovery. The method was validated by the determination of the Se mass balance. The Se-amino acids accounted for 91 ± 8% of the total selenium (mean of 95 samples of seven tissues analysed over a period of 18 months). The method was applied to the discrimination of the contribution of selenoproteins (containing SeCys) and other Se-containing proteins (containing SeMet) in tissues of animals during supplementation studies (dose–effect and tolerance).     

Spectroscopic and photophysical studies of the hydroquinone family of photochromic Schiff bases analyzed over a 17-orders-of-magnitude time scale

The hydroquinone family of photochromic Schiff bases has been studied by means of stationary and time-resolved spectroscopic absorption and emission techniques in the UV-Vis spectral range in the temporal range from 100 fs to 1 h. The studies have revealed that besides the ultrafast excited state intramolecular proton transfer reaction there is also another deactivation channel from the initially excited state. For the symmetric molecule with two intramolecular hydrogen bonds, the efficiency of the proton transfer reaction has been found to be at least ten times reduced when compared to that of the asymmetric molecule with one intramolecular hydrogen bond. The long-lived transient species absorbing in the UV range and coexisting with the photochrome have been observed in differently interacting solvents. Evidence for different conformers of almost all of the tautomers involved in the photochromic cycle has been also found.     

A general stereoselective method for the synthesis of cyclopropanecarboxylates. A new version of the homologous Horner-Wadsworth-Emmons reaction

The synthesis of alpha-, beta- and gamma-substituted alpha-phosphono-gamma-lactones was accomplished using different ring closure and ring homologation strategies. It was found that the lactones could be selectively transformed into the corresponding ethyl cyclopropanecarboxylates by treatment with sodium ethoxide in boiling THF. The reported reaction provides an attractive alternative to the classical homologous Horner-Wadsworth-Emmons approach to the construction of cyclopropanes with electron-withdrawing functionalities.     

An efficient synthesis of the phytoestrogen 8-prenylnaringenin from isoxanthohumol with magnesium iodide etherate

Xanthohumol was isolated from supercritical carbon dioxide-spent hop and transformed into isoxanthohumol. The demethylation of isoxanthohumol with the best yield 93% occurred when MgI₂ etherate in anhydrous THF was applied. Salts such as MgBr₂, MgCl₂, CaI₂, Mg(OAc)₂, Mg(OMe)₂ were also investigated. A convenient method for the xanthohumol isolation from supercritical carbon dioxide-spent hop is also described.     

Selective generation of lithiated benzonitriles: the importance of reaction conditions

Lithiated benzonitriles can be generated in high yields from reactions of bromobenzonitriles with n-BuLi in THF under standard cryogenic conditions (ca. -70 degrees C) provided the reverse addition mode is employed. The resultant aryllithiums are fairly stable at temperatures up to -60 degrees C. The formation of lithiated benzonitriles via Br/Li exchange under normal addition mode conditions is plagued by deprotonation and extensive CN-addition reactions. The generation of related aryllithiums from disilylated bromobenzonitriles is comparatively less sensitive to reaction conditions.     

Effect of UVC radiation on conformational restructuring of human serum albumin

The study of the influence of UVC-254 nm radiation on spectroscopic and calorimetric properties of human serum albumin in aqueous solutions was conducted. This radiation did not only accelerate aging of albumin solutions but also caused the other qualitative changes. The dose dependent effect on conformational restructuring and thermal stability of albumin for exposure periods from 10 to 60 min was shown. The differences in response to UVC-irradiation between non-defatted and fatty acid-free albumins were found.     

Unlocking a (Pseudo)-Mechanically Interlocked Molecule with a Coronene “Shoehorn”

Mechanically interlocked molecules (MIMs) have gained increasing interest during the last decades, not only because of their aesthetic appeal, but also because their unique properties have allowed them to find applications in nanotechnology, catalysis, chemosensing and biomedicine. Herein we describe how a pyrene molecule with four octynyl substituents can be easily encapsulated within the cavity of a tetragold(I) rectangle-like metallobox, by template formation of the metallo-assembly in the presence of the guest. The resulting assembly behaves as a mechanically interlocked molecule (MIM), in which the four long limbs of the guest protrude from the entrances of the metallobox, thus locking the guest inside the cavity of the metallobox. The new assembly resembles a metallo-suit[4]ane, given the number of protruding long limbs and the presence of the metal atoms in the host molecule. However, unlike normal MIMs, this molecule can release the tetra-substituted pyrene guest by the addition of coronene, which can smoothly replace the guest in the cavity of the metallobox. Combined experimental and computational studies allowed the role of the coronene molecule in facilitating the release of the tetrasubstituted pyrene guest to be explained, through a process that we named “shoehorning”, as the coronene compresses the flexible limbs of the guest so that it can reduce its size to slide in and out the metallobox.     

Projected gradient algorithms for Hartree-Fock and density matrix functional theory calculations

We present projected gradient algorithms designed for optimizing various functionals defined on the set of N-representable one-electron reduced density matrices. We show that projected gradient algorithms are efficient in minimizing the Hartree-Fock or the Muller-Buijse-Baerends functional. On the other hand, they converge very slowly when applied to the recently proposed BBk (k=1,2,3) functionals [O. Gritsenko et al., J. Chem. Phys. 122, 204102 (2005)]. This is due to the fact that the BBk functionals are not proper functionals of the density matrix.     

Unexpected Factors Affecting the Kinetics of Guest Molecule Release from Investigation of Binary Chemical Systems Trapped in a Single Void of Mesoporous Silica Particles

In this work, we present results for loading of well-defined binary systems (cocrystal, solid solution) and untreated materials (physical mixtures) into the voids of MCM-41 mesoporous silica particles employing three different filling methods. The applied techniques belong to the group of “wet methods” (diffusion supported loading – DiSupLo ) and “solvent-free methods” (mechanical ball-mill loading – MeLo , thermal solvent free – TSF ). As probes for testing the guest1-guest2 interactions inside the MCM-41 pores we employed the benzoic acid ( BA ), perfluorobenzoic acid ( PFBA ), and 4-fluorobenzoic acid ( 4-FBA ). The guests intermolecular contacts and phase changes were monitored employing magic angle spinning (MAS) NMR Spectroscopy techniques and powder X-ray diffraction (PXRD). Since mesoporous silica materials are commonly used in drug delivery system research, special attention has been paid to factors affecting guest release kinetics. It has been proven that not only the content and composition of binary systems, but also the loading technique have a strong impact on the rate of guests release. Innovative methods of visualizing differences in release kinetics are presented.