Numerical study of colloidal suspensions of soft spherical particles using the network method. 1. DC electrophoretic mobility

The electrophoretic mobility of a spherical particle coated with a uniformly charged permeable membrane and suspended in a general electrolyte solution is calculated numerically. The network simulation method used makes it possible to solve the problem without any restrictions on the values of the parameters such as the membrane thickness, fixed charge density in the membrane, viscous drag in the membrane, number and valence of the ionic species, and electrolyte concentration. The theoretical model used is similar to the one presented by Ohshima (H. Ohshima, J. Colloid Interface Sci. 228 (2000) 190), except for the inclusion in the force balance equation of an additional term corresponding to the force exerted by the liquid on the core of the moving particle. This inclusion is theoretically proven in the limiting case of a nonconducting suspending medium, in which the equation system can be analytically solved. The results obtained coincide with existing analytical expressions when the electrolyte concentration is high, the membrane is thick, and its resistance to the fluid flow is high.     

Chemometric study of selected polychlorinated biphenyls in ambient air of Madrid (Spain)

The formation of Fe(III) and Fe(II) chelates with pyridylazo and thiazolylazo reagents was examined. Optimum conditions for the formation of Fe(III) and Fe(II) chelates with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) were in detail evaluated. The LC method for simultaneous separation of Fe(III) and Fe(II) ions as 5-Br-PADAP chelates was evaluated using the PEEK column with C18 e.c. stationary phase and acetonitrile+water (90:10, v/v) eluent containing the 1x10(-3) mol l(-1) C(12)H(25)SO(3)Na, the ion-pairing reagent, pH 3.4-3.6. The simultaneous determination of 20-500 mug l(-1) Fe(II) ions (detection at 555 nm) and 20-500 mug l(-1) Fe(III) ions (detection at 585 nm) as 5-Br-PADAP chelates (for both ions, detection limit, 18 mug l(-1) for 20 mul loop) was established. The chromatographic method was applied to the water analysis. Although the present method is able to determine both Fe(III) and Fe(II) ions, the Fe(III) ion was not detected in all water samples. The Fe(II) was detected only in fresh gathered oligocene water at the level of 135 mug l(-1). The present method was used to the investigation of the distribution of Fe(III)/Fe(II) ions in aqueous and micellar solutions after action of external, ultrasonic field.     

A Large Volume Injection Procedure for GC-MS Determination of PAHs and PCBs

A simple on-column injection system for large volume of liquid samples for the GC-MS determination of traces of PAHs and PCBs has been investigated. A deactivated fused silica capillary 20 m × 0.53 mm I.D. and 2 meters of an HP5 column (0.53 mm,1 m film thickness) were used as retention gaps. Injection volumes of 80 L for PAHs and 90 L for PCBs, allow determination of 5–50 ng L^–1 PAHs and 11–44 ng L^–1 PCBs in hexane solution with an RSD of < 10%. The method has been used for the determination of PCBs and PAHs in soil sample.     

Synthesis of 4-aryl-2,3,6,7-tetrahydro-1H-pyrimido[4,5-b][1,4]-diazepin-6-ones from 4,5-diamino-1H-pyrimidin-6-ones and 1-aryl-3-(dimethylamino)-1-propanones

The reaction of 1-aryl-3-(dimethylamino)-1-propanones 1 with one equivalent of 4,5-diamino-1H-pyrimidin-6-ones 2 , in acidic medium, leads to the formation of 4-aryl-2,3,6,7-tetrahydro-1H-pyrimido[4,5-b]-[1,4]diazepin-6-ones 3 . The structure elucidation of the products is based on detail nmr analysis of experiments such as ¹³C, ¹H and DEPT including selective ¹³C{¹H} decoupling experiments.     

Cyclopentane-1,3-dione bis(4-methylthiosemicarbazone) monohydrochloride as a spectrophotometric reagent for the determination of chlorate in perchloric acid medium

1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride produces colored solutions with chlorate ions in strongly acid medium. The yellow color obtained has been used to propose a spectrophotometric method of C10₃^? determination in the concentration range 0.5–6.0 ppm (molar absorptivity 1.26 × 10⁴ liters mol^?1 cm^?1 at a wavelength of 397 nm).     

Adsorption of crude oil on anhydrous and hydrophobized vermiculite

This publication reports the adsorption of crude oil on vermiculite samples, expanded and hydrophobized with carnauba (Copernícia Cerífera) wax. The adsorption studies were performed by using columns filled with the vermiculite matrices and by dispersion of the vermiculite samples in an oil-water (50 ppm of oil) emulsion. The hydrate vermiculite exhibits a very low adsorption capacity against crude oil. On the other hand, anhydrous (expanded) and hydrophobized matrices show a high adsorption capacity. The 10% hydrophobized matrix show a 50% increased adsorption capacity, in comparison with the expanded one. For adsorption performed in the water-oil emulsion, saturation of the solid hydrophobized matrix is achieved after 60 min. The hydrophobized samples exhibit adsorption factors in the 0.7-1.0 range.     

Exo-metal coordination by a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 dimer in [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (2-NC5H4 = 2-pyridyl, C5H5N = pyridine)

The in situ reaction of the phosphazane dimer [CIP(mu-N-2-NC5H4)]2 (2) with CuCl in the presence of CsH5N/H2O gives the title complex [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (1), containing a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 ligand which is isoelectronic with species of the type [(P(mu-NR))2NR]2.     

Antiferromagnetism of poly(3-dodecylthiophene) irradiated by γ-beams

The magnetic properties of poly(3-dodecyl-thiophene) (PDDT) irradiated by -beams have been studied by measuring the magnetic susceptibility and EPR spectra. The irradiated PDDT is characterized, similarly as the non-irradiated one, by an antiferromagnetic course of magnetic susceptibility with a Néel temperature of 237 K. It is suggested that the antiferromagnetic properties of PDDT are caused by transformation of polarons to bipolarons, which takes place at lower temperatures.     

Theoretical Evaluation of Steric Effects in [ReH(5)(PR(3))(2)(SiR(3))(2)] Complexes with the IMOMM Method

A theoretical study including full geometry optimizations is carried out at the IMOMM(MP2:MM3) (IMOMM = integrated molecular orbital molecular mechanics) computational level on the [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] systems, the results being compared with available experimental diffraction data, as well as with MP2 results on the model system [ReH(5)(PH(3))(2)(SiH(3))(2)]. A simple scheme for the analysis of the relative weight of different contributions to the "steric" distortion is also proposed and applied to the same [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] species.     

Preparation of pentahalophenyl p-tolylisocyanide complexes of gold(I) and their reactions with amines,ammonia and alcohols

(Pentahalophenyl) (p-tolylisocyanide)gold(I) complexes were prepared by treating Au(C₆X₅) (tetrahydrothiophen) (X = F, Cl or Br) with p-MeC₆H₄NC. Their reactivity toward nucleophiles was studied and found to decrease in the sequence: primary amines > ammonia > secondary amines > aromatic amines > alcohols; the effects of the various C₆X₅ groups were less pronounced, but decreased according to C₆F₅ > C₆Cl₅ > C₆Br₅.Twenty-five novel gold(I) carbene derivatives were isolated.