Equation of state of nonadditive d-dimensional hard-sphere mixtures

An equation of state for a multicomponent mixture of nonadditive hard spheres in d dimensions is proposed. It yields a rather simple density dependence and constitutes a natural extension of the equation of state for additive hard spheres proposed by us [A. Santos, S. B. Yuste, and M. Lopez de Haro, Mol. Phys. 96, 1 (1999)]. The proposal relies on the known exact second and third virial coefficients and requires as input the compressibility factor of the one-component system. A comparison is carried out both with another recent theoretical proposal based on a similar philosophy and with the available exact results and simulation data in d=1, 2, and 3. Good general agreement with the reported values of the virial coefficients and of the compressibility factor of binary mixtures is observed, especially for high asymmetries and/or positive nonadditivities.     

Synthesis and Characterization of [(1,4‐diamine)dichloro]platinum(II) Compounds Preliminary Studies on their Biological Activity

Two 1,4‐diamine ligands were synthesized having 1,2‐bis(aminomethyl)‐cyclohexane and 1,2‐bis(aminomethyl)‐benzene structures. The two ligands have different electron density in the six‐membered ring: a cyclohexane versus a phenyl ring. The organic synthesis of the ligands was carried out by synthetic pathways of seven and four steps, respectively, starting from 1,2,3,6‐tetrahydrophthalic anhydride and diethyl phthalate. The coordination of platinum to these ligands afforded platinum(II) complexes which are analogue to the clinical drug cisplatin but form a seven‐membered chelate ring. The interaction of the platinum compounds with DNA was studied in order to know the relationship between the electron density of ligands and their capability to chelate DNA, by using three techniques: Circular Dichroism, Agarose Gel Electrophoresis and Atomic Force Microscopy. The degree of interaction of both compounds with DNA was slightly different, but both complexes showed a cisplatin‐like behaviour and are promising candidates to follow an extensive study of their cytotoxic activity.     

Effects of the attractive interactions in the thermodynamic, dynamic, and structural anomalies of a two length scale potential

Using molecular dynamic simulations, we study a system of particles interacting through a continuous core-softened potentials consisting of a hard core, a shoulder at closest distances, and an attractive well at further distance. We obtain the pressure-temperature phase diagram of this system for various depths of the tunable attractive well. Since this is a two length scale potential, density, diffusion, and structural anomalies are expected. We show that the effect of increasing the attractive interaction between the molecules is to shrink the region in pressure in which the density and the diffusion anomalies are present. If the attractive forces are too strong, particle will be predominantly in one of the two length scales and no density of diffusion anomaly is observed. The structural anomalous region is present for all the cases.     

Photoinduced ligand transformations in a ruthenium complex of dimethoxytetrapyridotetraazapentacene

The dinuclear ruthenium(II) complex [(phen)(2)Ru(tatpOMe)Ru(phen)(2)](4+) (2(4+); phen is 1,10-phenanthroline and tatpOMe is 10,21-dimethoxy-9,10,20,33-tetraazatetrapyrido[3,2-a:2'3'-c:3',2'-l:2',3'-n]pentacene) has been synthesized and characterized by (1)H NMR, ESI mass spectroscopy and elemental analysis. Loss of methoxy group from bridging ligand of complex 2(4+) due to irradiation is observed by (1)H NMR and photochemistry. The interrelated electronic properties UV-Vis, electrochemistry, photochemistry and molecular orbital calculation are analyzed and discussed on the bridging ligand of the complex 2(4+).     

Antiproliferative activity, antioxidant capacity and tannin content in plants of semi-arid northeastern Brazil

The objective of this study was to evaluate antiproliferative activity, antioxidant capacity and tannin content in plants from semi-arid northeastern Brazil (Caatinga). For this study, we selected 14 species and we assayed the methanol extracts for antiproliferative activity against the HEp-2 (laryngeal cancer) and NCI-H292 (lung cancer) cell lines using the (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazole) (MTT) method. In addition, the antioxidant activity was evaluated with the DPPH (2,2-diphenyl-2-picrylhydrazyl) assay, and the tannin content was determined by the radial diffusion method. Plants with better antioxidant activity (expressed in a dose able to decrease the initial DPPH concentration by 50%, or IC50) and with higher levels of tannins were: Poincianella pyramidalis (42.95±1.77 μg/mL IC50 and 8.17±0.64 tannin content), Jatropha mollissima (54.09±4.36μg/mL IC50 and 2.35±0.08 tannin content) and Anadenanthera colubrina (73.24±1.47 μg/mL IC50 and 4.41±0.47 tannin content). Plants with enhanced antiproliferative activity (% living cells) were Annona muricata (24.94±0.74 in NCI-H292), Lantana camara (25.8±0.19 in NCI-H292), Handroanthus impetiginosus (41.8±0.47 in NCI-H292) and Mentzelia aspera (45.61±1.94 in HEp-2). For species with better antioxidant and antiproliferative activities, we suggest future in vitro and in vivo comparative studies with other pharmacological models, and to start a process of purification and identification of the possible molecule(s) responsible for the observed pharmacological activity. We believe that the flora of Brazilian semi-arid areas can be a valuable source of plants rich in tannins, cytotoxic compounds and antioxidant agents.     

Photosensitizing properties of triplet beta-lapachones in acetonitrile solution

The photochemical reactivity of β-lapachone ( 1 ), nor -β-lapachone ( 2 ) and 1,2-naphthoquinone ( 3 ) towards amino acids and nucleobases or nucleosides has been examined employing the nanosecond laser flash photolysis technique. Excitation (λ = 355 nm) of degassed solutions of 1 – 3 , in acetonitrile, resulted in the formation of their corresponding triplet excited states. These transients were efficiently quenched by l -tryptophan, l -tryptophan methyl ester, l -tyrosine, l -tyrosine methyl ester and l -cysteine ( k _q  ≈ 10⁹ L mol⁻¹ s⁻¹). For l -tryptophan, l -tyrosine and their methyl esters new transients were formed in the quenching process, which were assigned to the corresponding radical pair resulting from an initial electron transfer from the amino acids or their esters to the excited quinone, followed by a fast proton transfer. No measurable quenching rate constants could be observed in the presence of thymine and thymidine. On the other hand, efficient rate constants were obtained when 1 – 3 were quenched by 2'-deoxyguanosine ( k _q  ≈ 10⁹ L mol⁻¹ s⁻¹). The quantum efficiency of singlet oxygen (¹O₂) formation from 1 to 3 was determined employing time-resolved near-IR emission studies upon laser excitation and showed considerably high values in all cases (Φ_Δ = 0.6), which are fully in accord with the ππ* character of these triplets in acetonitrile.     

Biosurfactant Production by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> Grown in Residual Soybean Oil

Pseudomonas aeruginosa PACL strain, isolated from oil-contaminated soil taken from a lagoon, was used to investigate the efficiency and magnitude of biosurfactant production, using different waste frying soybean oils, by submerged fermentation in stirred tank reactors of 6 and 10 l capacities. A complete factorial experimental design was used, with the goal of optimizing the aeration rate (0.5, 1.0, and 1.5 vvm) and agitation speed (300, 550, and 800 rpm). Aeration was identified as the primary variable affecting the process, with a maximum rhamnose concentration occurring at an aeration rate of 0.5 vvm. At optimum levels, a maximum rhamnose concentration of 3.3 g/l, an emulsification index of 100%, and a minimum surface tension of 26.0 dynes/cm were achieved. Under these conditions, the biosurfactant production derived from using a mixture of waste frying soybean oil (WFSO) as a carbon source was compared to production when non-used soybean oil (NUSO), or waste soybean oils used to fry specific foods, were used. NUSO produced the highest level of rhamnolipids, although the waste soybean oils also resulted in biosurfactant production of 75–90% of the maximum value. Under ideal conditions, the kinetic behavior and the modeling of the rhamnose production, nutrient consumption, and cellular growth were established. The resulting model predicted data points that corresponded well to the empirical information.     

Thermal characterization of hydrotalcite used in the transesterification of soybean oil

Hydrotalcite was synthesised by co-precipitation method, calcined and characterized by XRD, BET, IR and TG/DTA/DTG analyses and tested as solid base catalyst in the transesterification of soybean oil with methanol, achieving a methyl ester content of 99.5%. The thermal decomposition of hydrotalcite calcined occurred in four mass loss steps at 28, 105, 203 and 400 °C. The hydrotalcite was recovered and through a simple evaluation by TG/DTA/DTG techniques it was found that at 500 °C is the temperature, where the organic matter should be eliminated from the catalyst. This study shows the importance of thermal analysis in the evaluation of the recovery temperature of hydrotalcite.