Extended class of metric tensors in relativity

An extended metric tensor that is a function of an internal vectory ^a(x) leads to a spin-1 massless field of gravitational origin. It is shown that this new field vanishes in the linear approximation for the extended metric.On leave of absence from the Universidade de Brasilia.     

The Antiepileptic Lamotrigine and Its Analogues: Comparative Theoretical Electronic Properties

Electronic properties of lamotrigine (LTG) and two analogues (A1 and A2) are compared through MOPAC-AM1 calculations. Two stable conformers of LTG are calculated to exist in agreement with X-ray crystallography. In the three compounds and the two conformers for each of them, the more favorable protonation sites are N₂ and N₄; these should then be the sites appropriate for interaction with a receptor, and group valence reinforces the supposition. The molecular electrostatic potentials show that a region between the two chlorine atoms in LTG could be the site for an electrostatic interaction with a corresponding site in the receptor. The fluorine atom in A1 would play an equivalent role. A simple model for LTG-receptor interaction is proposed.     

Thermoanalytical study of glibenclamide and excipients

Summary Taking into account the problems of desertification and agricultural practices able to provide income to the population at the semi-arid region of North-East Brazil, this work presents the results of the chemical and thermal characterization by TG and DSC of the seed derivatives of Cnidoscolus quercifolius, hereinafter called faveleira, aiming at the application of these materials as an alternative of food source for animals and for the human population at this region. The faveleira seed derivatives present thermodynamic properties similar to the ones of other foods utilized for human use, as well as an acceptable calorific value. According to TG and DSC results, was verified that the faveleira derivatives presents good thermal and oxidative stabilities.     

Studies on the encapsulation of diclofenac in small unilamellar liposomes of soya phosphatidylcholine

The encapsulation of acid (AD) and sodium diclofenac (SD) in small unilamellar liposomes (SUV) as well as the interactions of the drug with the bilayer was studied. SUV was prepared by sonication from multilamellar liposomes containing soya phosphatidylcholine and diclofenac at various proportions. The size distribution obtained from dynamic light scattering showed that the incorporation of SD decreases significantly the size of the liposomes suggesting that the drug interacts with the bilayer of the liposomes. This size decrease is related with the phase transition of liposomes to mixed micelar solution. The encapsulation of the hydrophilic dye indocyanine green in the aqueous compartment of liposomes showed that the rate of captured dye decreases with SD concentration suggesting the transition of liposomes to mixed micelles. The (31)P NMR analysis indicates that SD interacts with the phosphate of phosphatidylcholine head groups. A schematic model for interaction of SD with phosphatidylcholine of the liposomes in which the diclofenac anion interacts with the ammonium group of the phospholipid and the dichlorophenyl ring occupies a more internal site of bilayer near phosphate group was proposed.     

Polystyrene/thermoplastic starch blends with different plasticizers

Conventional plastics has a large impact in increasing the environment’s pollution. That’s why the interest has turned towards novel partially and completely biodegradable polymers. In this work, blends of polystyrene and thermoplastic starch with glycerol and Buriti (Mauritia flexuosa L.) oil as plasticizers were prepared. Samples were analyzed using TG/DTG and DSC techniques. The TG results indicated that the blends with Buriti oil are thermally more stable than those with glycerol. The DSC analysis that Buriti oil provides a higher degree of plasticization of PS, compared to the blends plasticized using glycerol under the studied conditions.     

Determination of salicylate in blood serum using an amperometric biosensor based on salicylate hydroxylase immobilized in a polypyrrole-glutaraldehyde matrix

The use of an amperometric biosensor for the salicylate determination in blood serum is described. The biosensor is based on salicylate hydroxylase (EC 1.14.13.1) electropolymerized onto a glassy carbon-working electrode with polypyrrole and glutaraldehyde, to improve the biosensor lifetime. The hexacyanoferrate (II) was also incorporated to work as a redox mediator to minimize possible interferences. The salicylate is enzymatically converted to catechol, which is monitored amperometrically by its electrooxidation at+0.170 V versus SCE (saturated calomel electrode). Salicylate determination was carried out maintaining the ratio between beta-NADH and salicylate at 4:1 (30 degrees C). The amperometric response of the biosensor was linearly proportional to the salicylate concentration between 2.3x10(-6) and 1.4x10(-5) mol l(-1), in 0.1 mol l(-1) phosphate buffer (pH 7.8), containing 0.1 mol l(-1) KCl and 5.0x10(-4) mol l(-1) Na(2)H(2)EDTA, as supporting electrolyte. The recovery studies, in the presence of several interfering compounds, showed recoveries between 96.4 and 104.8%. The useful lifetime of the biosensor in the concentration range evaluated was at least 40 days, in continuous use. Blood serum samples analyzed by this biosensor showed a good correlation compared to the spectrophotometric method (Trinder) used as reference, presenting relative deviations lower than 7.0%.     

Analysis of sediments for heavy metals by a rapid electrothermal atomic-absorption procedure

A rapid electrothermal atomic-absorption spectrophotometric procedure with homogenization as the only pretreatment is compared with two wet pretreatment methods followed by flame atomic-absorption, in a statistically designed experiment. Samples from the top 5 cm of sediments at three different points of the Tejo estuary were used for the tests. The results show that the electrothermal procedure performed as well as whichever was the better of the flame methods for the determination of cadmium and nickel, irrespective of the sand content of the samples; although not statistically significant, there was apparently a decrease in recovery for chromium, copper and lead by the electrothermal method as the sand content of the sample increased. For zinc the electrothermal method gave results statistically different from those of the flame procedures when the sand content was high but not when the organic content of the sample was high. Because of the limited degree of replication (5 variates) the relative differences between the average values obtained by the three methods were significant only if they exceeded 15%. The electrothermal method has the advantage of substantially greater speed.     

Spectroscopic and electrochemical studies on (2-hydroxypicolinate)-bis(2,2′-bipyridine)ruthenium(II) and related complexes

Summary The synthesis, spectra and electrochemistry of [Ru(bipy)₂-(picOH)]⁺ and -picO-[Ru(bipy)₂]₂ ²⁺ (bipy = 2,2-bipyridine and picOH = 3-hydroxypicolinate ion) are described. The spectroscopic properties in the visible region are dominated by the intense Ru bipy chargetransfer transitions. In the binuclear complex, the two [Ru(bipy)₂L]²⁺ moieties are nonequivalent, exhibiting E _1/2 = 0.69 and 1.20 V versus s.h.e. The partially oxidized species exhibits a weak intervalence transfer band at 1085 nm, and is consistent with a Robin-Day class II mixed valence complex.     

New Factorial Designs to Evaluate Chemisorption of Divalent Metals on Aminated Silicas

Adsorption processes of Cu(II), Co(II), and Hg(II) on two aminated silica gel surfaces with immobilized ethylenediamine and diethylenediamine groups were studied by a new 2(3) full factorial design. Two metal quantity levels, temperatures of 25 and 50 degrees C, and silica amounts of 100 and 200 mg were employed. Our study indicates that higher factorial design levels increase adsorption for all metals evaluated, with the exception of the mass parameter. Adsorption is also significantly affected by important antagonistic and synergistic effects involving all factors. Both functionalized silica gel surfaces present higher interactions and good perspectives in preconcentration studies for mercury. The factorial design results are also discussed in terms of some solvation properties for each of the metals studied. Copyright 2001 Academic Press.     

A New ent‐Kaurane Diterpene from Stems of Alibertia macrophylla K. Schum. (Rubiaceae)

Phytochemical investigations of the stems of a specimen of Alibertia macrophylla led to the isolation and characterization of the new diterpene ent‐kaurane‐2β,3α,16α‐triol ( 1 ), along with triterpenes 2 – 8 , iridoids 9 – 12 , and phenolic acids 13 – 15 . The structure of 1 was established based on spectroscopic studies (¹H‐ and ¹³C‐NMR, IR, and HR‐ESI‐MS). This is the first report of the isolation of a diterpene from the Alibertia genus in Rubiaceae.