Dodekahydro‐closo‐dodekaborate der schweren Erdalkalimetalle aus wäßriger Lösung: Ca(H2O)7[B12H12] · H2O,Sr(H2O)8[B12H12] und Ba(H2O)6[B12H12]

Dodecahydro‐ closo ‐dodecaborates of the Heavy Alkaline‐Earth Metals from Aqueous Solution: Ca(H₂O)₇[B₁₂H₁₂] · H₂O, Sr(H₂O)₈[B₁₂H₁₂], and Ba(H₂O)₆[B₁₂H₁₂] The crystalline hydrates of the heavy alkaline earth metal dodecahydro‐closo‐dodecaborates (M[B₁₂H₁₂] · n H₂O, n = 6–8; M = Ca, Sr, Ba) are easily accessible by reaction of an aqueous (H₃O)₂[B₁₂H₁₂] solution with an alkaline earth metal carbonate (MCO₃). By isothermic evaporation of the respective aqueous solution we obtained colourless single crystals which are characterized by X‐ray diffraction at room temperature. The three compounds Ca(H₂O)₇[B₁₂H₁₂] · H₂O (orthorhombic, P2₁2₁2₁; a = 1161.19(7), b = 1229.63(8), c = 1232.24(8) pm; Z = 4), Sr(H₂O)₈[B₁₂H₁₂] (trigonal, R3; a = 1012.71(6), c = 1462.94(9) pm; Z = 3) and Ba(H₂O)₆[B₁₂H₁₂] (orthorhombic, Cmcm; a = 1189.26(7) pm, b = 919.23(5) pm, c = 1403.54(9) pm; Z = 4) are neither formula‐equal nor isostructural. The structure of Sr(H₂O)₈[B₁₂H₁₂] is best described as a NaCl‐type arrangement, Ba(H₂O)₆[B₁₂H₁₂] rather forms a layer‐like and Ca(H₂O)₇[B₁₂H₁₂] · H₂O a channel‐like structure. In first sphere the alkaline earth metal cations Ca²⁺ and Sr²⁺ are coordinated by just seven and eight oxygen atoms from the surrounding water molecules, respectively. A direct coordinative influence of the quasi‐icosahedral [B₁₂H₁₂]^2– cluster anions becomes noticeable only for the Ba²⁺ cations (CN = 12) in Ba(H₂O)₆[B₁₂H₁₂]. The dehydratation of the alkaline earth metal dodecahydro‐closo‐dodecaborate hydrates has been shown to take place in several steps. Thermal treatment leads to the anhydrous compounds Ca[B₁₂H₁₂], Sr[B₁₂H₁₂] and Ba[B₁₂H₁₂] at 224, 164 and 116 °C, respectively.     

Development and validation of an HPLC method for the simultaneous determination of tocopherols, tocotrienols and carotenoids in cereals after solid-phase extraction

The increasing interest in antioxidant properties of cereal and cereal-based products has prompted the development of a simple and reliable HPLC method for the simultaneous determination of important phytochemicals like tocopherols (T), tocotrienols (T3) and carotenoids. Separation was carried out on a Nucleosil 100 C(18) column, 5 μm (250 mm × 4.6 mm) thermostated at 25 °C, using a linear gradient elution system starting with methanol and ending with a mixture of methanol-isopropanol-acetonitrile. All separated compounds including the internal standard (α-tocopherol acetate) were eluted within 16 min and detected by dual detection: fluorescence for tocopherols and tocotrienols at 290 nm excitation and 320 nm emission and UV-vis photodiode array detection for lutein and β-carotene at 450 nm. Detection limits ranged from 0.2 μg/g (β-carotene) to 1.60 μg/g (α-tocopherol). The intra- and inter-assay coefficients of variation were calculated by using cereals with different levels of lipophilic antioxidants. The extraction method involved sample saponification and clean-up by solid-phase extraction (SPE). The extraction recoveries obtained using OASIS HLB SPE cartridges and dichloromethane as eluent were in the range of 90.2-110.1%, with RSD lower than 10%. The method was successfully applied to cereals: durum wheat, bread wheat, rice, barley, oat, rye, corn and triticale.     

DFT-calculated structures based on 1H NMR chemical shifts in solution vs. structures solved by single-crystal X-ray and crystalline-sponge methods: Assessing specific sources of discrepancies

DFT calculations of ¹H NMR chemical shifts, using various functionals and basis sets, the conductor-like polarizable continuum model and discrete solute-solvent hydrogen bond interactions have been used to derive the solution structures of methyl salicylate and methyl 2,5-dihydroxybenzoate. We demonstrate that very good agreement between experimental and computed ¹H NMR chemical shifts can be obtained for various basis sets. The DFT structures in solution were compared with the recently reported X-ray structure, solved by the crystalline-sponge method, of the methyl salicylate and the single-crystal X-ray structure of methyl 2,5-dihydroxybenzoate. It is demonstrated that the information provided by ¹H NMR chemical shifts about the solution structure is significantly more precise than that obtained by the single-crystal X-ray and the crystalline-sponge methods.     

Local density inhomogeneities and dynamics in supercritical water: A molecular dynamics simulation approach

Molecular dynamics atomistic simulations in the canonical ensemble (NVT-MD) have been used to investigate the "Local Density Inhomogeneities and their Dynamics" in pure supercritical water. The simulations were carried out along a near-critical isotherm (Tr = T/Tc = 1.03) and for a wide range of densities below and above the critical one (0.2 rho(c) - 2.0 rho(c)). The results obtained reveal the existence of significant local density augmentation effects, which are found to be sufficiently larger in comparison to those reported for nonassociated fluids. The time evolution of the local density distribution around each molecule was studied in terms of the appropriate time correlation functions C(Delta)rhol(t). It is found that the shape of these functions changes significantly by increasing the density of the fluid. Finally, the local density reorganization times for the first and second coordination shell derived from these correlations exhibit a decreasing behavior by increasing the density of the system, signifying the density effect upon the dynamics of the local environment around each molecule.     

Poly{dl-lactide-b-[oligo(ethylene glycol) methyl ether (meth)acrylate)]} block copolymers. Synthesis,characterization, micellization behavior in aqueous solutions and encapsulation of model hydrophobic compounds

A series of well-defined poly{dl -lactide-b-[oligo(ethylene glycol) methyl ether (meth)acrylate)]} (PDLLA-b-POEG[M]A) functional amphiphilic diblock copolymers was synthesized by employing a multistep procedure involving: (a) ring-opening polymerization of dl -lactide using n-decanol and stannous octoate as the initiating system, (b) esterification reaction of the PDLLA hydroxyl end groups with 2-bromoisobutyryl bromide, (c) atom transfer radical polymerization of OEG(M)A with the newly created bromoisobutyryl initiating site, and (d) incorporation of biotin or folic acid at the POEGA chain ends using click chemistry. The products were characterized by NMR spectroscopy and SEC analysis. The aggregation behavior of the synthesized block copolymers was investigated by dynamic light scattering at 25°C in aqueous solutions. The hydrophobic model compounds Nile red and pyrene were efficiently incorporated into the copolymer aggregates in aqueous solutions. High partition coefficient values were determined by fluorescence spectroscopy.     

Expeditious copper-catalyzed conjugate 1,4-addition of bromo[2-(1,3-dioxolan-2-yl)ethyl]magnesium to alpha,beta-cycloalkenones and subsequent transformations

Expeditious CuI-catalyzed conjugate 1,4-addition of bromo[2-(1,3-dioxolan-2-yl)ethyl]magnesium to the five-, six-, seven-, and eight-membered alpha,beta-cycloalkenones is described. The reaction times are decreased dramatically compared to CuBr-(CH(3))(2)S catalysis. The resulting ketoacetals were subsequently cyclized to bicyclic beta-hydroxy ketones and alpha,beta-enones, followed by further transformations.     

Approaches to primary tert-alkyl amines as building blocks

Primary tert-alkyl amines include analogues of amantadine, a fragment commonly linked to pharmacophoric groups to enhance biological activity. The preparation of primary tert-alkyl amines is considered to be a difficult problem. Four synthetic procedures, some of which have been previously reported for the synthesis of amines with primary (RCH₂NH₂) or secondary (RR'CHNH₂) alkyl and/or aryl groups, were tested for the synthesis of primary tert-alkyl amines (RR′R″CNH₂) in aliphatic series including adamantane adducts. These procedures included the formation and reduction of tert-alkyl azides, the Ritter reaction in standard and modified conditions, the addition of organometallic reagents to N-tert-butyl sulfinyl ketimines and one-pot reactions between nitriles and organometallic reagents in the presence of a Lewis acid, Τi(iPrO)₄ or CeCl_3. These synthetic routes are unexplored for primary tert-alkyl amines. Studies on the synthetic routes for primary tert-alkyl amines are currently lacking. The reaction conditions and substrate limitations were studied for each procedure, with the first procedure being the most general and applicable also for compounds bearing bulky adducts.     

Impact of biological factors on binding media identification in art objects: identification of animal glue in the presence of Aspergillus niger

The materials and especially organic materials used for creation of art objects can be utilized by various microorganisms for their growth and facilitate the microbial colonization of the object. An understanding of the chemical alterations in artefacts caused by the presence of microorganisms can be crucial for correct identification of the materials initially used for the artefact creation--nowadays an important step in restoration and/or art-historical investigation of the art object. The present article describes a model experiment in which we investigated the possible chemical alterations in animal glue films used as substrate for growth of the fungus Aspergillus niger. The sterilized animal glue solution was poured into Petri dishes, inoculated with Aspergillus niger, and subsequently incubated at 15 degrees C for 0, 7, 9, 14, and 28 days. After interruption of incubation, the content of the Petri dish was analyzed for amino acid composition by the GC-MS based method. It was found that the growth of Aspergillus niger on animal glue films did not cause significant changes in the amino acid composition of the film and had no impact on animal glue identification.