Monte Carlo Study of Structural and Thermodynamic Properties of Liquid Chloroform Using a Five Site Model

A five site potential model combining Lennard–Jones plus Coulomb potential functions has been developed for chloroform molecule. The partial charges needed for Coulombic interactions were derived using the chelpg procedure implemented in the gaussian 92 program. These calculations were performed at the MP2 level with MC-311G* basis set for Cl and 6-311G** for C and H atoms. The parameters for the Lennard–Jones potentials were optimized to reproduce experimental values for the density and enthalpy of vaporization of the pure liquid at 298 K and 1 atm. The statistical mechanics calculations were performed with the Monte Carlo method in the isothermic and isobaric (NpT) ensemble. Besides the values obtained for density, ρ, and molar enthalpy of vaporization at constant pressure, Δ H_V, for liquid chloroform, results for molar volume, V_m, molar heat capacity, C_p, isobaric thermal expansivity, α_p, and isothermal compressibility, κ_T, for this pure liquid are also in very good agreement with experimental observations. Size effects on the values of thermodynamic properties were investigated. The potential model was also tested by computing the free energy for solvating one chloroform molecule into its own liquid at 298 K using a statistical perturbation approach. The result obtained compares well with the experimental value. Site–site pair correlation functions were calculated and are in good accordance with theoretical results available in the literature. Dipole–dipole correlation functions for the present five site model were also calculated at different carbon–carbon distances. These correlations were compared to those obtained using the four site model reported in the literature. An investigation of the solvent dependence of the relative free energy for cis/trans conversion of a hypothetical solute in TIP4P water and chloroform was accomplished. The results show strong interaction of water and chloroform molecules with the gauche conformer. The value obtained for the free energy barrier for cis/trans rotation in TIP4P water is higher than that for chloroform. This result is in agreement with the continuous theory for solvation as the conformer with higher dipole moment is more favoured by the solvent with higher dieletric constant. The results also show an increase in entropy as the solute goes from the cis to the trans geometry and this result is more appreciable in the aqueous solution. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the Modeling of Some Anti-inflammatory and Anti-thrombotic Drugs by AM1

Two families of autacoids from cell membrane phospholipids have been identified. The first, the icosanoids, which are formed from arachidonic acid, include prostaglandins and leukotrienes. The other includes modified phospholipids, as the platelet aggregating factor (PAF). These compounds are related to inflammatory and cardiovascular diseases. We review in this paper some of the work that has been done in our laboratories in the last few years relating to the modeling of new potential thromboxane synthase (TXS) and 5-lipoxygenase (5-LO) and cyclooxygenase (COX) inhibitors, and TXA₂ receptor antagonists derived from nitrogenated heterocycles. We include the results of the modeling of a group of proposed PAF antagonists, and compare their structures with PAF itself and with a recently proposed PAF antagonist model. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytoplankton composition and abundance of a central Amazonian floodplain lake

The phytoplankton community of Lake Camaleão, a smallfloodplainlake influenced by a large whitewater river, the Solimões, was monthlyinvestigated for the composition and abundance of itsphytoplankton. The seasonal influence of the floodregime on biomass, species richness and diversity, andits relation with physical and chemical factors(temperature, pH, dissolved oxygen, electricalconductivity, total seston and inorganic nutrients)was analyzed and subjected to principal componentanalysis. Diversity was variable along the seasonalcycle: relatively high values were observed at the endof the dry season supported by high nutrientconcentrations. The phytoplankton was comprised of 262 taxa,with strong dominanceof euglenoids (81%). The three sample stations did not differamong each other, except in the dry season, due todata cluster in relation to theprincipal axis (1 and 2), explaining 63% of thevariation. Biomass accumulation as a function of lakearea reduction contributed to theseresults, indicating that the phytoplankton dynamicswere hydrology-driven.     

Catecholamine and MHPG plasma levels,platelet MAO activity,and3H-imipramine binding in heroin and cocaine addicts

This work evaluated in a population of heroin and heroin plus cocaine human addicts:

1. Norepinephrine (NE), epinephrine (Epi), and 3-methoxy-4-hydroxyphenylglycol (MHPG) (the principal metabolite of brain NE) plasma levels;
2. Monoamine oxidase (MAO) activity; and
3. ³H-imipramine specific binding to the amine carrier in platelets.

NE plasma levels were significantly lower in the short-term heroin user groups (1–3 and 4–6 yr), a finding not observed in both the long-term heroin user (>6 yr) and heroin plus cocaine user (>6 yr) groups. Epi levels changed in a similar manner, except that a significant increase was noted in heroin plus cocaine abusers. Conversely, dopamine and MHPG plasma levels increased with the duration of heroin use, and even more with cocaine abuse. Platelet MAO activity increased in all groups. Specific³H-imipramine binding sites showed an increase after 3 yr of heroin abuse and in all heroin plus cocaine addicts. In conclusion, short-term use of heroin decreases NE or Epi release, but with prolonged use, a slow adpatation occurs. In contrast, cocaine inhibits the neuronal Epi uptake, even in a situation of long duration of abuse. Probably the amine levels additionally regulate the amine carrier, resulting in changes that show a different pattern from major depression. These drugs of abuse may also influence directly or indirectly related enzymatic systems.     

VIP enhances TRH-stimulated prolactin secretion of pituitary tumours. Studies with 31P NMR

Intravenous thyrotrophin releasing hormone (TRH) caused a 6.5-fold increase in plasma prolactin (PRL) in rats carrying implanted pituitary tumours. Vasoactive intestinal polypeptide (VIP) had no effect, but TRH given after VIP raised TRH stimulated secretion 13-fold above basal. 31P NMR spectroscopy showed that VIP caused a decrease in high energy metabolites (depleted phosphocreatine, elevated inorganic phosphate and lowered intracellular pH). TRH alone caused a similar but smaller effect; given after VIP, it caused no detectable depletion. We suggest that the changes in high energy metabolite concentrations reflect increased cellular energy consumption consistent with a priming process (stage 1) in PRL secretion, followed by hormone release (stage 2). VIP induces stage 1 whereas RTH induced both stages.     

Clavispora,a new yeast genus of the Saccharomycetales

In Candida lusitaniae van Uden et do Carmo-Sousa (1959), strains of opposite sex have been found. Cells of the opposite mating types conjugate and form asci with one to four clavate spores. These are easily liberated from the ascus. The type strain of Candida obtusa (Dietrichson) van Uden et do Carmo-Sousa ex van Uden et Buckley (1970) also produces ascospores after mating with one of the strains of Candida lusitaniae. As clavate ascospores are unknow in yeasts, a new genus, Clavispora, is proposed with Clavispora lusitaniae spec. nov. as type species.     

Studies of the mechanisms for the induction of in vivo tumor immunity. VI. Induction of specific and nonspecific cell-mediated immunity in tumor-bearing hosts and its correlation with transplantation tumor immunity

Studies were performed to determine the development of cell-mediated cytotoxic response at tumor site in C57BL/6 mice bearing progressively growing FBL-3 ascites leukemia. The effectors isolated from tumor ascites are found to be highly cytotoxic for leukemic target cells. The levels of cytotoxicity obtained with effectors isolated from tumor site are generally higher than those obtained with immune mice. This cytotoxicity is both specific and nonspecific. The specific cytotoxicity against tumor-associated antigen is mainly mediated by T cells and the nonspecific cytotoxicity against unrelated tumor cells is mediated largely by macrophages. The T-cell-enriched preparation did not give significant natural killer activity. When testing the ability of these effectors to produce in vivo immunity against the challenge of FBL-3, it was found that only T cells could confer the transplantation-type immunity, but the immunity was transient. The macrophage-enriched preparation isolated from tumor ascites failed to give in vivo protection. These findings indicate that in FBL-3 system, mice with progressively growing tumors are able to develop immune response against tumor cells. However, this immunity is probably interfered with by a suppressor factor(s) or suppressor cells which restrict their activity to eliminate the tumor cells effectively.     

Prevalence, biotypes, plasmid profile and antimicrobial resistance of Campylobacter isolated from wild and domestic animals from northeast Portugal.

The incidence of Campylobacter jejuni and Campylobacter coli in wild and producing animals has been studied to evaluate their importance as potential reservoirs of campylobacter infection. These organisms were isolated from: 59 chicken (60.2%), 65 swine (59.1%), 31 black rats (57.4%), 61 sparrows (45.5%), 21 ducks (40.5%), 32 cows (19.5%) and 27 sheep (15.3%). Biotypes, plasmid and resistance profiles were studied in order to characterize the isolates. Biotypes I and II of C. jejuni were predominant in all reservoirs except swine, where C. coli I was more frequent. Plasmid prevalence was higher in strains isolated from swine (53.8%) and rats (45.5%). The size of the plasmids ranged from 1.3 to 82 MDa. A 2.3 MDa plasmid was the most frequent, detected in all the reservoirs except ducks. Antimicrobial susceptibility testing revealed that 5.5% of the strains were resistant to ampicillin, 5.5% to tetracycline, 12.6% to erythromycin and 23.5% to streptomycin. Resistance to erythromycin (26.2%) and to streptomycin (58.4%) was particularly high in isolates from swine. Tetracycline resistance was encoded by a 33 or a 41 MDa plasmid and transferred by conjugation.