A simple analysis of the influence of the solvent-induced electronic polarization on the N-15 magnetic shielding of pyridine in water

Electronic polarization induced by the interaction of a reference molecule with a liquid environment is expected to affect the magnetic shielding constants. Understanding this effect using realistic theoretical models is important for proper use of nuclear magnetic resonance in molecular characterization. In this work, we consider the pyridine molecule in water as a model system to briefly investigate this aspect. Thus, Monte Carlo simulations and quantum mechanics calculations based on the B3LYP/6-311++G (d,p) are used to analyze different aspects of the solvent effects on the N-15 magnetic shielding constant of pyridine in water. This includes in special the geometry relaxation and the electronic polarization of the solute by the solvent. The polarization effect is found to be very important, but, as expected for pyridine, the geometry relaxation contribution is essentially negligible. Using an average electrostatic model of the solvent, the magnetic shielding constant is calculated as -58.7 ppm, in good agreement with the experimental value of -56.3 ppm. The explicit inclusion of hydrogen-bonded water molecules embedded in the electrostatic field of the remaining solvent molecules gives the value of -61.8 ppm.

Counter-ion effect on surfactant-DNA gel particles as controlled DNA delivery systems

The ability to entrap drugs within vehicles and subsequently release them has led to new treatments for a number of diseases. Based on an associative phase separation and interfacial diffusion approach, we developed a way to prepare DNA gel particles without adding any kind of cross-linker or organic solvent. Among the various agents studied, cationic surfactants offered particularly efficient control for encapsulation and DNA release from these DNA gel particles. The driving force for this strong association is the electrostatic interaction between the two components, as induced by the entropic increase due to the release of the respective counter-ions. However, little is known about the influence of the respective counter-ions on this surfactant-DNA interaction. Here we examined the effect of different counter-ions on the formation and properties of the DNA gel particles by mixing DNA (either single-(ssDNA) or double-stranded (dsDNA)) with the single chain surfactant dodecyltrimethylammonium (DTA). In particular, we used as counter-ions of this surfactant the hydrogen sulfate and trifluoromethane sulfonate anions and the two halides, chloride and bromide. Effects on the morphology of the particles obtained, the encapsulation of DNA and its release, as well as the haemocompatibility of these particles are presented, using counter-ion structure and DNA conformation as controlling parameters. Analysis of the data indicates that the degree of counter-ion dissociation from the surfactant micelles and the polar/hydrophobic character of the counter-ion are important parameters in the final properties of the particles. The stronger interaction with amphiphiles for ssDNA than for dsDNA suggests the important role of hydrophobic interactions in DNA.

Effect of hydroalcoholic extract from Copaifera langsdorffii leaves on urolithiasis induced in rats

Copaifera langsdorffii Desf. commonly known as "copaiba", produce a commercially valuable oil-resin that is extensively used in folk medicine for anti-inflammatory, antimicrobial and antiseptic purposes. We have found the hydroalcoholic extract of this plant leaf has the potential to treat urolithiasis, a problem affecting similar to 7% of the population. To isolate the functional compounds C. langsdorffii leaves were dried, ground, and macerated in a hydroalcoholic solution 7:3 to produce a 16.8% crude extract after solvent elimination. Urolithiasis was induced by introduction of a calcium oxalate pellet (CaOx) into the bladders of adult male Wistar rats. The treated groups received the crude extract by oral gavage at 20 mg/kg body weight daily for 18 days. Extract treatment started 30 days after CaOx seed implantation. To monitor renal function sodium, potassium and creatinine concentrations were analyzed in urine and plasma, and were found to be in the normal range. Analyses of pH, magnesium, phosphate, calcium, uric acid, oxalate and citrate levels were evaluated to determine whether the C. langsdorffii extract may function as a stone formation prevention agent. The HPLC analysis of the extract identified flavonoids quercitrin and afzelin as the major components. Animals treated with C. langsdorffii have increased levels of magnesium and decreased levels of uric acid in urinary excretions. Treated animals have a significant decrease in the mean number of calculi and a reduction in calculi mass. Calculi taken from extract treated animals were more brittle and fragile than calculi from untreated animals. Moreover, breaking calculi from untreated animals required twice the amount of pressure as calculi from treated animals (6.90 +/- A 3.45 vs. 3.00 +/- A 1.51). The extract is rich in flavonoid heterosides and other phenolic compounds. Therefore, we hypothesize this class of compounds might contribute significantly to the observed activity.