Thermogravimetric and calorimetric evaluation of babassu biodiesel obtained by the methanol route

The growing petroleum deficit requires the development of alternative fuel sources. Biodiesel is a good alternative, as it is a biodegradable and renewable product, which obeys the carbon cycle. In this work, the biodiesel from babassu was synthesized using the methanol route, and characterized by physico-chemical analyses in order to make able the investigated biodiesel to fulfill with its properties the requirements of Brazilian National Agency for Petroleum, Natural Gas and Biofuel (ANP). Besides gas chromatography, IR spectroscopy experiments and thermoanalytical measurements in air and in nitrogen were done to determine the main thermal decomposition processes and calorimetric events. The evaporation temperature of babassu biodiesel was similar in both atmospheres, started around 52 in air and around 60°C in nitrogen.     

Spectral assignments of new diterpenes from Hyptis martiusii Benth

The structural characterization of two new abietanes and a new spiro-fused tricyclic diterpene isolated from the roots of Hyptis martiusii is described. The first member of a new class of rearranged abietane diterpenoids designated martiusane was characterized by the use of 1D NMR and several 2D shift correlated NMR pulse sequences (1H,1H-COSY, HMQC, HMBC and NOESY). Unambiguous 1H and 13C chemical shift assignments for all compounds are reported.     

Molecular modeling of freezing of simple fluids confined within carbon nanotubes

We report Monte Carlo simulation results for freezing of Lennard-Jones carbon tetrachloride confined within model multiwalled carbon nanotubes of different diameters. The structure and thermodynamic stability of the confined phases, as well as the transition temperatures, were determined from parallel tempering grand canonical Monte Carlo simulations and free-energy calculations. The simulations show that the adsorbate forms concentric molecular layers that solidify into defective quasi-two-dimensional hexagonal crystals. Freezing in such concentric layers occurs via intermediate phases that show remnants of hexatic behavior, similar to the freezing mechanism observed for slit pores in previous works. The adsorbate molecules in the inner regions of the pore also exhibit changes in their properties upon reduction of temperature. The structural changes in the different regions of adsorbate occur at temperatures above or below the bulk freezing point, depending on pore diameter and distance of the adsorbate molecules from the pore wall. The simulations show evidence of a rich phase behavior in confinement; a number of phases, some of them inhomogeneous, were observed for the pore sizes considered. The multiple transition temperatures obtained from the simulations were found to be in good agreement with recent dielectric relaxation spectroscopy experiments for CCl(4) confined within multiwalled carbon nanotubes.     

Compatibility and Stability Studies of Propranolol Hydrochloride Binary Mixtures and Tablets for TG and DSC-photovisual

This study demonstrates the thermalanalysis applications in compatibility and stability studies of the propranolol binary mixture sand tablets A and B. The propranolol binary mixtures were prepared in the laboratory and compared to the fully formulated tablets using the thermogravimetric (TG) and calorimetric(DSC) methods. DSC of binary mixtures showed similar phase transition to propranolol drug. The tablets phase transition decreased and there was no detectable significant interaction in propranolol–lactose mixture and tablets. The DSC-photovisual test revealed an interaction similar to the Maillard reaction. The TG isothermal study showed a difference in the profile between the drug and tablets due excipients quality and problems in manufacture process. The kinetic parameters indicated a lower stability for the tablets than propranolol drug. The thermal techniques thermally differentiated the propranolol preparations demonstrating the importance in the design development of pharmaceuticals solid-dosage form. This revised version was published online in July 2006 with corrections to the Cover Date.     

Subtle reactivity patterns of non-heteroatom-substituted manganese alkynyl carbene complexes in the presence of phosphorus probes

The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR'(3; 3a: R = R'= Ph, 3b: R = Ph, R'= Tol, 3c: R = Tol, R'= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR' (R'= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R' (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PPh2Me)R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R')PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R')H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R')=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R')=CHC(R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13' is proposed.     

Analysis of methylglyoxal in water and biological matrices by capillary zone electrophoresis with diode array detection

We describe a new method for the determination of methylglyoxal in water and biological matrices, using o-phenylenediamine as derivatizing agent and solid-phase extraction followed by capillary zone electrophoresis with diode array detection. 25 mM sodium phosphate running buffers at pH 2.2, 30 kV, and 25 degrees C allowed the best instrumental conditions for the optimum separation of methylglyoxal in a suitable analytical time (< 10 min), using an uncoated fused-silica capillary of 75 microm inner diameter and an effective length of 45.1 cm with an extended light path and the wavelength set to 200 nm. Under optimized instrumental conditions, good reproducibility of the migration time (< 1.1%), precision (< 5%), an excellent linear dynamic range from 0.1 to 3.6 mg/L (r(2) = 0.9997), and low limits of detection (7.2 microg/L) were obtained for methylglyoxal measurements, using the internal standard methodology. Assays on laboratory-spiked tap and ground water samples allowed a remarkable accuracy, presenting yields of 95.0 +/- 4.3 and 94.0 +/- 1.1%, respectively, and good performance to determine methylglyoxal in beer and yeast cells suspensions matrices was also obtained at trace level. The present methodology is a cost-effective alternative for routine quality control analysis, showing to be reliable, sensitive, and with a low sample volume requirement to monitor methylglyoxal in water and biological matrices.     

Determination of atracurium and laudanosine in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method coupled with fluorometric detection has been developed for the determination of atracurium and its major end-product laudanosine in human plasma. The method enables good separation of atracurium from its metabolites after direct precipitation of plasma proteins. The assay is sensitive, reproducible and linear for atracurium concentrations ranging from 31.25 to 8000 ng/ml. In a clinical setting, drugs commonly administered during anesthesia did not interfere with the assay. This method provides a simple and time-saving alternative to existing methods.     

Réaction du diméthylcuprate de lithium avec les dérivés carbonylés α,β-insaturés α-fluorés et α-chlorés

Depending on the nature of the halogen, α-fluoro- and α-chloro-α,β-unsaturated carbonyl compounds (whose reduction potentials are greater than ? 2.4V) react in different ways with lithium dimethylcuprate. With α-fluoro derivatives, both 1,2- and 1,4-addition is observed, their ratios depend on the steric hindrance of the β-position. 1,4-Addition products are obtained from aldehydes and β-monosubstituted α-chloro-α,β-ethylenic ketones and esters. β,β-Disubstituted α-chloro ketones and esters give only reduction of halogen via halogen-metal exchange.     

Normal mode double-branch dispersion relation for metals within a variational calculation

In a previous note [1] a variational calculation was considered which describes volume plasmons in highdensity metals. We extend this calculation by considering a more flexible parametrization and show that, as a result, a splitting is obtained leading to two normal modes for each value of the transferred momentum q. The single particle excitations are responsible for the new structure. The strength and the energy of each mode determine its collective or single particle character for very small or very large values of q. The present results predict an appreciable redistribution of transition strength, in agreement with recent experimental findings.