Intercalation of Benzamide into Kaolinite

Well-crystallized kaolinite (K) was initially reacted at 60 degrees C with a water/dimethylsulfoxide (DMSO) mixture and the resulting intercalation derivative (K-DMSO) was characterized by powder X-ray diffractometry (PXRD), thermal analysis (simultaneous TG and DSC), and Fourier-transformed infrared spectroscopy (FTIR). Benzamide crystals were then melted with the K-DMSO derivative at 140 degrees C for 4 days, when a gradual displacement of DMSO by benzamide was observed within the interlayer spacing of the modified kaolinite. The resulting material, after extensive washing with acetone, was characterized and compared to the results obtained previously for the K-DMSO composite. Benzamide intercalation proceeded by gradual displacement of DMSO molecules until completion. The structural stabilization of the K-BZ derivative was explained through the establishment of hydrogen bonds between the carbonyl oxygen atoms of the intercalated benzamide and aluminol groups present at the surface of the kaolinite layer. The interlamellar spacing of K-BZ was shown to be possibly occupied by benzamide molecules that were located at a 68 degrees orientation in relation to the layer surface. Unlike most intercalation molecules such as DMSO, variations in the interplanar spacing of kaolinite were consistent with the nonkeying of any other part of the molecule between the aluminosilicate interlayers. Copyright 2000 Academic Press.     

Vibrational infrared intensities and polar tensors of 1,2-difluoroethylenes

The polar tensors of cis and trans-1,2-difluoroethylenes have been determined with new normal modes based in a reassignment of nu(7) and nu(12) bands of the trans isomers and frequency values corrected for Fermi resonances and phase shifts. The signs of the dipole moment derivatives (and its directions, for B(u) symmetry species) were considered to be those of MP2/6-31G** estimates. Root mean square errors calculated for the new tensor element values from each pair of isotopomers (trans-1,2-C(2)H(2)F(2)/trans-1,2-C(2)D(2)F(2) and cis-1,2-C(2)H(2)F(2)/cis-1,2-C(2)D(2)F(2)) show that the new polar tensor sets fit the isotopic invariance criterion better than previously reported sets. The accuracy of polar tensor transference procedures was tested by calculating the infrared intensities of trans-1,2-C(2)H(2)F(2) through the new polar tensors of the cis isomer. The resulting estimates are very accurate and also support the new band assignment, though the A(6) intensity remains still somewhat underestimated.     

Ester synthesis catalyzed by Mucor miehei lipase immobilized on magnetic polysiloxane-polyvinyl alcohol particles

Mucor miehei lipase was immobilized on magnetic polysiloxane-polyvinyl alcohol particles by covalent binding with high activity recovered. The performance of the resulting immobilized biocatalyst was evaluated in the synthesis of flavor esters using heptane as solvent. The impact on reaction rate was determined for enzyme concentration, molar ratio of the reactants, carbon chain length of the reactants, and alcohol structure. Ester synthesis was maximized for substrates containing excess acyl donor and lipase loading of 25 mg/mL. The biocatalyst selectivity for the carbon chain length was found to be different concerning the organic acids and alcohols. High reaction rates were achieved for organic acids with 8 or 10 carbons, whereas increasing the alcohol carbon chain length from 4 to 8 carbons gave much lower esterification yields. Optimal reaction rate was determined for the synthesis of butyl caprylate (12 carbons). Esterification performance was also dependent on the alcohol structure, with maximum activity occurring for primary alcohol. Secondary and tertiary alcohols decreased the reaction rates by more than 40%.     

Diagnosing broken ergodicity using an energy fluctuation metric

The Mountain and Thirumalai energy fluctuation metric, Omega(t), has been used to study the effective ergodicity of 60- and 256-atom binary Lennard-Jones mixtures in order to determine the reliability of the calculated diffusion constants at different energies. A plot of Omega(t) against 1time allows the identification of two distinct regimes: ergodic supercooled liquids, where Omega(t) approaches zero, and nonergodic glassy states, where Omega(t) asymptotically approaches a nonzero value on the molecular dynamics time scale. This approach seems to be more appropriate than attempting to define a threshold value for Omega(t)/Omega(0). The behavior of systems between these two limits, which are nonergodic on the time scale considered but may be approaching ergodicity, was examined for a range of simulation times. The calculated diffusion constants change as effective ergodicity is approached, moving closer to the Vogel-Tammann-Fulcher fit defined by higher-energy systems that are already considered to be effectively ergodic. Using the form of the decay of the metric as a measure of ergodicity, we have been able to reproduce the trend in fragility obtained by Sastry for a 256-atom system [Nature (London) 409, 164 (2001)], correcting some of our earlier results [J. Chem. Phys. 120, 8314 (2004)].     

Synthesis, characterization and thermal studies on solid compounds of 2-chlorobenzylidenepyruvate of heavier trivalent lanthanides and yttrium(III)

Solid-state compounds of general formula LnL_3⋅nH₂O, where Ln represents heavier lanthanides and yttrium and L is 2-chlorobenzylidenepyruvate, have been synthesized. Chemical analysis, simultaneous thermogravimetry-differential analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, elemental analysis and infrared spectroscopy have been employed to characterize and to study the thermal behaviour of these compounds in dynamic air atmosphere. On heating these compounds decompose in four (Gd, Tb, Ho to Lu, Y) or five (Eu, Dy) steps. They lose the hydration water in the first step and the thermal decomposition of the anhydrous compounds up to 1200°C occurs with the formation of the respective oxide, Tb₄O₇ and Ln₂O₃ (Ln=Eu, Gd, Dy to Lu and Y) as final residue. The dehydration enthalpies found for these compounds (Eu, to Lu and Y) were: 65.77, 55.63, 86.89, 121.65, 99.80, 109.59, 131.02, 119.78, 205.46 and 83.11 kJ mol^-1, respectively.     

Mass spectrometric characterization of two novel inflammatory peptides from the venom of the social wasp Polybia paulista

The social wasp P. paulista is relatively common in southeast Brazil causing many medically important stinging incidents. The seriousness of these incidents is dependent on the amount of venom inoculated by the wasps into the victims, and the characteristic envenomation symptoms are strongly dependent on the types of peptides present in the venom. In order to identify some of these naturally occurring peptides available in very low amounts, an analytical protocol was developed that uses a combination of reversed-phase and normal-phase high-performance liquid chromatography (HPLC) of wasp venom for peptide purification, with matrix-assisted laser desorption/ionization time-of-flight post-source decay mass spectrometry (MALDI-Tof-PSD-MS) and low-energy collision-induced dissociation (CID) in a quadrupole time-of-flight tandem mass spectrometry (QTof-MS/MS) instrument for peptide sequencing at the sub-picomole level. The distinction between Leu and Ile was achieved both by observing d-type fragment ions obtained under CID conditions and by comparison of retention times of the natural peptides and their synthetic counterparts (with different combinations of I and/or L at N- and C-terminal positions). To distinguish the isobaric residues K and Q, acetylation of peptides was followed by Q-Tof-MS analysis. The primary sequences obtained were INWLKLGKMVIDAL-NH(2) (MW 1611.98 Da) and IDWLKLGKMVMDVL-NH(2) (MW 1658.98 Da). Micro-scale bioassay protocols characterized both peptides as presenting potent hemolytic action, mast cell degranulation, and chemotaxis of polymorphonucleated leukocyte (PMNL) cells. The primary sequences and the bioassay results suggest that these toxins constitute members of a new sub-class of mastoparan toxins, directly involved in the occurrence of inflammatory processes after wasp stinging.     

Study of the diclofenac/phospholipid interactions with liposomes and monolayers

The interaction of diclofenac sodium (SD) with soya phosphatidylcholine (SPC) has been studied with floating Langmuir monolayers and liposomes. SD was either introduced into the subphase of SPC monolayers or co-spread with SPC on an aqueous subphase. In both cases, SD caused the surface pressure isotherm to become more expanded, thus demonstrating the affinity between SD and SPC. The incorporation of SD caused SPC liposomes to have a decreased diameter according to light scattering experiments. When SPC liposomes were injected into an aqueous subphase, their destruction yielding surface-active monomers could be monitored by changes in surface pressure. SD-loaded liposomes displayed a much faster kinetics when the surface density of surface-active monomers was plotted against time, with rate constants increasing significantly with the SD concentration. The kinetic profile can be quantitatively analyzed by plotting ln[1 - (gamma/gamma infinity)] versus t1/2.     

Analysis of beers from Brazil with synchrotron radiation total reflection X-ray fluorescence

Summary In this study the concentrations of P, S, Cl, K, Ca, Mn, Fe, Zn and Br in twenty-nine brands of national and international beers were determined by synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF). The results were compared with the limits established by the Brazilian legislation and the nutritional values established by National Agricultural Library (NAL, USA). The measurements were performed at the X-Ray Fluorescence Beamline at Brazilian National Synchrotron Light Laboratory, in Campinas, S?o Paulo, Brazil, using a polychromatic beam for excitation. A small volume of 5 ml of beers containing an internal standard used to correct geometry effects was analyzed without pretreatment. The measuring time was 100 seconds and the detection limits obtained varied from 1 mg ^. l^-1 for Mn and Fe to 15 mg ^. l^-1 for P.     

Hydrolytic protein cleavage mediated by unusual mononuclear copper(II) complexes: X-ray structures and solution studies

The crystal structures and redox and UV-vis/EPR spectroscopic properties of two new mononuclear copper(II) complexes, [Cu(HL1)Cl2] (1) and [Cu(L1)Cl] (2), prepared through the reaction between copper(II) chloride and the ligand 2-[(bis(pyridylmethyl)amino)methyl]-4-methyl-6-formylphenol (HL1) under distinct base conditions, are reported along with solution studies. Also, we demonstrate that these CuII complexes are able to cleave unactivated peptide bonds from bovine serum albumin (BSA) and the thermostable enzyme Taq DNA polymerase at micromolar concentration, under mild pH and temperature conditions. The cleavage activity seems to be specific with defined proteolytic fragments appearing after protein treatment. The location of the specific cleavage sites was tentatively assigned to solvent-accessible portions of the protein. These are two of the most active Cu(II) complexes described to date, since their cleavage activity is detected in minutes and evidence is here presented for a hydrolytic mechanism mediating protein cleavage by these complexes.