ESR, electrochemical and reactivity studies of antitrypanosomal palladium thiosemicarbazone complexes

Cyclic voltammetry (CV) and electron spin resonance (ESR) techniques were used in the investigation of novel palladium complexes with bioactive thiosemicarbazones derived from 5-nitrofurane or 5-nitrofurylacroleine. Sixteen palladium complexes grouped in two series of the formula [PdCl(2)HL] or [PdL(2)] were studied. ESR spectra of the free radicals obtained by electrolytic reduction were characterized and analyzed. The ESR spectra showed two different hyperfine patterns. The stoichiometry of the complexes does not seem to affect significantly the hyperfine constants however we observed great differences between 5-nitrofurane and 5-nitrofurylacroleine derivatives. The scavenger properties of this family of compounds were lower than Trolox.     

Organoboron Schiff bases as cell‐staining fluorescent probes: Synthesis,Chemio‐photophysical characterization,DFT, and X‐ray structures

The fluorescence imaging technologies are becoming the most powerful and noninvasive diagnostic tools in cellular biology and modern medicine where abnormal cell arrangements are associated with diseases. Thus, these techniques require new fluorescent dyes with excellent chemical, physical, and photophysical properties. A series of four new Boron Schiff bases ( 1 – 4 ) has been prepared by condensation between phenylboronic acid with the corresponding ligand. The compounds were characterized by NMR (¹H, ¹³C, and ¹¹B), UV/vis, fluorescence spectroscopy, and high‐resolution mass spectrometry. The crystal structures of three compounds showed tetracoordinated Boron atoms with semiplanar skeleton ligands. Interesting organoboron response to viscosity on their fluorescence (Φ: more than 3‐fold). Additionally, compounds 1 and 2 were found to serve as a fluorescent dye for cell imaging (B16F10, CaCo, and A‐431 cells) since it has the capability to rapidly accumulate within the cells and gave bright green fluorescence, it showed low cytotoxicity activity and high photostability in solution. Additionally, the compounds have also been investigated using DFT.     

Meso-structure formation for enhanced organic photovoltaic cells

[reaction: see text] Formation of a controlled fullerene mesophase within an organic host system has enabled us to create high-power conversion efficiency photovoltaics. This mesophase is formed using thermal gradients that provide a fluidic mobility of the fullerenes allowing for greater dispersion of nanocrystalline 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)C61 (PCBM) within regioregular poly(3-hexylthiophene) (P3HT). From this reorganization of the component materials in the matrix the overall efficiency of the system jumps dramatically from the roughly 2.4% to 5.2%.     

Temperature inhomogeneities simulated with multiparticle-collision dynamics

The mesoscopic simulation technique known as multiparticle collision dynamics is presented as a very appropriate method to simulate complex systems in the presence of temperature inhomogeneities. Three different methods to impose the temperature gradient are compared and characterized in the parameter landscape. Two methods include the interaction of the system with confining walls. The third method considers open boundary conditions by imposing energy fluxes. The transport of energy characterizing the thermal diffusivity is also investigated. The dependence of this transport coefficient on the method parameters and the accuracy of existing analytical theories is discussed.     

Driving forces and polymer hydrodynamics in the Soret effect

A temperature gradient induces different driving forces on the components of a mixture which translates into their segregation. We show that these driving forces constitute the physical picture behind the thermodiffusion effect, and provide an alternative expression of the Soret coefficient which can be applied to both colloidal suspensions and molecular mixtures. To verify the validity of the formalism, we quantify the related forces in an Eulerian reference frame by non-equilibrium molecular simulations. Furthermore, we present an analytical argument to show that the hydrodynamic interactions need to be accounted for to obtain the proper scaling of the thermophoretic force. This result combined with the presented expression satisfactorily explains the experimentally known size dependence of the thermodiffusion coefficient in dilute polymer solutions.     

The whole is more than the sum of its parts: Modeling community-level effects of UVR in marine ecosystems

The effect of UVB radiation (UVBR, 290-320 nm) on the dynamics of the lower levels of the marine plankton community was modeled. The model was built using differential equations and shows a good fit to experimental data collected in mesocosms (defined as large enclosures of 1500 L filled with natural marine waters). Some unexpected results appear to be possible by indirect effects in prey (bacteria, phytoplankton and heterotrophic flagellates). In particular, apparent competition appears between small phytoplankton and bacteria. This effect is caused by a shared predator (ciliates). Another remarkable effect is an increase in bacteria and flagellates populations due to enhanced UVBR. This effect is similar to that observed under mesocosm experimental conditions and is related to the decrease of predation due to the direct damage to predators (ciliates) by UVBR. The effect of UVBR changing interaction coefficients may be dramatic on the community structure, producing big changes in equilibrium populations, as demonstrated by sensitivity analysis of the model. In order to generalize these results to field conditions it will be necessary to increase model complexity and include extra organic mater sources, mixing and sinking effects and predation by large zooplankton. This work shows that UVBR may produce community global responses that are consequence of both direct and indirect effects among populations.     

Six-membered tetracarbonylmanganese(I) and -rhenium(I) metalacycles containing the [Ph2P(Se)NP(Se)Ph2] ligand: solution and solid state characterization

The halocarbonyls BrM(CO)₅, M = Mn and Re, were reacted with the KN(SePPh₂)₂ salt in equimolar amounts; the reactions were thermally carried out and resulted in the generation of the hexacoordinated isostructural complexes [M(CO)₄{Ph₂P(Se)NP(Se)Ph₂-Se,Se′}] with a twist MSePNPSe ring conformation. Complexes’ characterizations were achieved by IR, mass, NMR (¹H, ¹³C, ³¹P, ⁷⁷Se) spectroscopies, and by single-crystal X-ray diffraction.     

Electrochemical study of the herbicide Tribenuron Determination in commercial samples

 The herbicide Tribenuron has been investigated. It has an acidic character with a pKa value of 4.1. Hydrolysis was confirmed and its rate increased with temperature and acidity, light influence was not observed. Electrochemical characteristics of this compound have been studied at pH values from 1 to 7 by applying DC, TAST and DP polarography as well as cyclic and differential pulse voltammetry at the HMDE. The reduction of Tribenuron occurs in two processes, the first at pH<7 and the second at pH<4. This study is devoted to the first process, which has been demonstrated to be irreversible and simultaneously governed by diffusion and adsorption phenomena. Both hydrolysis and polarographic reduction of Tribenuron yielded the same degradation products: 2-methoxycarbonylbenzenesulfonamide and 2-N-methyl-amino-4-methoxy-6-methyl-1,3,5-triazine. The quantitative determination of Tribenuron can be carried out by DPP with a detection limit of 92 μg/L or by adsorptive stripping voltammetry reaching a detection limit of 2.6 μg/L. Assays of commercial samples are described. Received: 3 June 1996 / Revised: 24 July 1996/Accepted: 24 July 1996