13C and 1H NMR signal assignments of some new synthetic dehydroabietic acid derivatives

The (1)H and (13)C NMR signal assignments of a series of new synthetic derivatives of dehydroabietic acid are presented.     

Titanium dioxide anatase as matrix for matrix-assisted laser desorption/ionization analysis of small molecules

The use of inorganic species as assisting materials in matrix-assisted laser desorption/ionization (MALDI) analysis is an alternative approach to avoid interfering matrix ions in the low-mass region of the mass spectra. Reports of the application of inorganic species as matrices in MALDI analysis of small molecules are, however, scarce. Nevertheless, titanium dioxide (TiO(2)) powder has been reported to be a promising matrix medium. In this study we further explore the use of TiO(2) as a matrix for the MALDI analysis of low molecular weight compounds. We present results showing that nanosized TiO(2) anatase and TiO(2) rutile perform better as MALDI matrices than a commercial TiO(2) anatase/rutile mixture. Moreover, when using nanosized TiO(2) anatase as a matrix, high-quality mass spectra can be obtained with strong analyte signals and weak or non-existing matrix interference ions. Furthermore, our results show that the phase type plays an important role in the application of TiO(2) as a MALDI matrix.     

New approach to exclusive formation of both enantiomers of β-amino acid derivatives

A highly selective two-step approach to chiral β-amino esters via the hydride reductive amination of chiral allenes is reported. β-Enamino esters were obtained from the nucleophilic addition of amines to 2,3-allenoates bearing a chiral auxiliary. The reduction of the (1R)-(−)-10-phenylsulfonylisobornyl β-enamino esters gave the corresponding β-amino esters with S configuration whereas the reduction of the (1S)-(+)-10-phenylsulfonylisobornyl β-enamino esters led to β-amino esters with R configuration. The rationalization of the observed selectivity was supported by semi-empirical molecular orbital calculations (PM3).     

Synthesis of the C7-C24 fragment of (−)-Macrolactin F

An enantioselective and convergent synthesis of the C7-C24 fragment of Macrolactin F was achieved from four main fragments. A hydrotelluration/transmetalation sequence was used to install the E,Z diene present in the molecule, while a hydrozirconation/transmetalation sequence was used to connect two advanced intermediates.     

Methods and Supports for Immobilization and Stabilization of Cyclomaltodextrin Glucanotransferase from Thermoanaerobacter

Thermoanaerobacter cyclomaltodextrin glucanotransferase (CGTase) was immobilized using different supports and immobilization methods to study the effect on activity recovery. The enzyme covalently attached into glyoxyl-silica showed low activity recovery of 1.5%. The hydrophobic adsorption of the enzyme on Octadecyl-Sepabeads yielded also low activity recovery, 3.83%, and the enzyme could easily leak from the support at low ionic strength, although the immobilization yield was satisfactory, approximately 76%. The CGTase encapsulated in a sol–gel matrix gave an activity recovery of 6.94% and maximum cyclization activity at 60 °C, at pH 6.0. The half-time life at 60 °C, pH 6.0, in the presence of substrate was 100 min, which was lower than that of the free enzyme. The best activity recovery in this work (6.94%) is approximately five times smaller than that obtained previously using glyoxyl-agarose as support and covalent immobilization. Thus, the best support and method we tested so far for immobilization of CGTase is covalent attachment on glyoxyl-agarose.     

Vibrational ground state properties of H(5)(+) and its isotopomers from diffusion Monte Carlo calculations

Diffusion Monte Carlo computations, with and without importance sampling, of the zero-point properties of H(5)(+) and its isotopomers using a recent high accuracy global potential energy surface are presented. The global minimum of the potential possesses C(2v) symmetry, but the calculations predict a D(2d) geometry for zero-point averaged structure of H(5)(+) with one H atom "in the middle" between two HH diatoms. The predicted zero-point geometries of the deuterated forms have H in the middle preferred over D in the middle and for a nonsymmetric arrangement of D atoms the preferred arrangement is one which maximizes the number of D as the triatomic ion. We speculate on the consequences of these preferences in scattering of H(2)+H(3)(+) and isotopomers at low energies, such as those in the interstellar medium.     

Shape controlled synthesis of CaMoO4 thin films and their photoluminescence property

CaMoO₄ (CMO) disordered and ordered thin films were prepared by the complex polymerization method (CPM). The films were annealed at different temperatures and time in a conventional resistive furnace (RF) and in a microwave (MW) oven. The microstructure and surface morphology of the structure were monitored by atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HRSEM). Order and disorder were characterized by X-ray diffraction (XRD) and optical reflectance. A strong photoluminescence (PL) emission was observed in the disordered thin films and was attributed to complex cluster vacancies. The experimental results were compared with density functional and Hartree-Fock calculations.     

On-line redox speciation analysis of antimony using l-proline immobilized on controlled pore glass and hydride generation inductively coupled plasma optical emission spectrometry for detection

l-proline was immobilized on controlled pore glass to study the ability of this material for the separation and preconcentration of Sb(III) and Sb(V). The substrate was packed in a minicolumn and incorporated in a flow injection system. The effluents of the on-line solid phase extraction (before and after elution) were directly coupled to the hydride generation inductively coupled plasma optical emission spectrometry system. The effect of pH, sample (and eluent) volume, flow rates of sample loading and elution on separation of Sb(III) e Sb(V) were evaluated. Our experiments demonstrated that Sb(V) was not retained and it was selectively determined during the loading step, while retained Sb(III) was determined after elution. The proposed system was also used for the selective preconcentration of Sb(III). In this case, a preconcentration factor of 11 and a limit of detection of 90 ng L⁻¹ for Sb(III) were achieved when 8 mL of sample were loaded into the column. The speciation analysis of inorganic Sb in river water and effluent samples was performed using the proposed method. The values obtained for total Sb (obtained by sum of Sb(III) and Sb(V)) were in good agreement with expected values. Recoveries of Sb(III) and Sb(V) in the river water Standard Reference Material 1640 (from National Institute of Standard and Technology) and spiked river waters were between 83 and 111%.     

C≡H ⋅<Emphasis Type="Italic">s</Emphasis> O Hydrogen Bonds in Small Ring Carbonyl Compounds: Vibrational Spectroscopy and <Emphasis Type="Italic">Ab initio</Emphasis> Calculations

The effect of the molecular structure on the properties of C-H⋅s O bonds was investigated in a set of small cyclic carbonyl compounds, using vibrational spectroscopy and ab initio calculations. Two main effects were studied: the size of the ring and the inclusion of oxygen atoms in the ring. The analysis of the band profile of the carbonyl stretching mode reveals the presence of single dimerization equilibria in the series cyclobutanone-cyclopentanone-cyclohexanone. The smallest cyclobutanone was found to have the lowest dimerization energy, with an experimental ΔH value of 3.7± 0.6 kJ mol⁻¹. The systems with oxygen atoms in the ring, γ-butyrolactone and ethylene carbonate were found to present more complex equilibria. Ab initio calculations suggest that this complexity is due to the presence of additional dimer structures and higher oligomers.     

Complete assignment of 1H and 13C NMR spectra of some 4'-substituted diethyl 1-methylthio- and diethyl 1-methylsulfonyl-2-oxo-2-phenylethylphosphonates

The complete assignment of 1H and 13C NMR spectra of some 4'-substituted diethyl 1-methylthio- and diethyl 1-methylsulfonyl-2-oxo-2-phenylethylphosphonates bearing as substituents methoxy, fluoro, chloro, bromo and nitro is reported.