Theoretical study of the role of solvent Stark effect in electron transitions

The possible influence of the solvent Stark effect (SSE) on the solvatochromic shift in electron transitions has been analyzed by using the ASEP/MD (averaged solvent electrostatic potential from molecular dynamics) method. With this purpose, four molecules, two polar (acrolein and formaldehyde) and two non-polar (p-difluorobenzene and trans-difluoroethene) have been studied in solvents of diverse polarity. Independently of the nature of the system we found that the contribution of SSE on the average value of the solvent shift or on the multipole moment values is negligible. In the case of centro-symmetric molecules, our results permit to discard the SSE as cause of the solvent shift found, which must be assigned to the electrostatic interaction of the solute quadrupole and higher multipoles with the solvent. As the SSE values provide also a measure of the errors introduced by the mean field approximation (MFA), these results indicate that MFA permits a very accurate determination of the solvent shift at the same time that it reduces drastically the computational cost. Finally, a new procedure suited to the ASEP/MD method has been presented that permits to estimate the inhomogeneous broadening of spectral bands, complementing the information provided by mean field theories. This procedure does not need additional quantum calculations and its computational cost is minimal.     

High-pressure dissociation of crystalline para-diiodobenzene: optical experiments and Car-Parrinello calculations

We have investigated the high-pressure properties of the molecular crystal para-diiodobenzene, by combining optical absorption, reflectance, and Raman experiments with Car-Parrinello simulations. The optical absorption edge exhibits a large red shift from 4 eV at ambient conditions to about 2 eV near 30 GPa. Reflectance measurements up to 80 GPa indicate a redistribution of oscillator strength toward the near-infrared. The calculations, which describe correctly the two known molecular crystal phases at ambient pressure, predict a nonmolecular metallic phase, stable at high pressure. This high-density phase is characterized by an extended three-dimensional network, in which chemically bound iodine atoms form layers connected by hydrocarbon bridges. Experimentally, Raman spectra of samples recovered after compression show vibrational modes of elemental solid iodine. This result points to a pressure-induced molecular dissociation process which leads to the formation of domains of iodine and disordered carbon.     

Improvement of plant parameters of the ROBO gamma irradiation facility due to design modification

Two industrial scale, “ROBO” type ⁶⁰Co gamma irradiation facilities have recently been put into operation in Syria and Peru, and the dosimetry commissioning of both plants have been carried out to determine dose distribution within products and to calculate plant parameters such as efficiency, dose uniformity ratio and throughput. There are some design modifications between the two plants in connection with the location of the carriers with respect to the source plaque and also to each other. The effect of these construction modifications on the plant parameters is discussed in the analysis of the dose distribution data measured in the carriers with depth and height among the four irradiation rows on both sides of the source plaque. The plant parameters were also calculated for different product densities using the technical data of the facilities, and the calculated and measured results were compared to each other.     

Synthesis,characterization and anticancer activity of new palladacycles derived from chiral α‐diimines

Optically pure α‐diimines quantitatively obtained in solvent‐free conditions starting from 2,3‐butanedione and (S)‐(?)‐1‐phenylethylamine and (S)‐(?)‐1‐(4‐methylphenyl)ethylamine, respectively, yielded the new chiral mono‐Pd complexes 2a–b, which have been partly characterized by IR, ¹H‐ and ¹³C‐NMR spectroscopies along with MS‐FAB⁺ spectrometry. The crystal and molecular structure for palladacycle 2a has been fully confirmed by single‐crystal X‐ray studies. Studies in vitro of 2a–b have displayed growth inhibition against different classes of cancer: leukemia (K‐562 CML), colon cancer (HCT‐15), breast cancer (MCF‐7), central nervous system (U‐251 Glio) and prostate cancer (PC‐3) cell lines. Copyright © 2009 John Wiley & Sons, Ltd.     

Electronic Tongues Employing Electrochemical Sensors

This review presents recent advances concerning work with electronic tongues employing electroanalytical sensors. This new concept in the electroanalysis sensor field entails the use of chemical sensor arrays coupled with chemometric processing tools, as a mean to improve sensors performance. The revision is organized according to the electroanalytical technique used for transduction, namely: potentiometry, voltammetry/amperometry or electrochemical impedance. The significant use of biosensors, mainly enzyme‐based is also presented. Salient applications in real problem solving using electrochemical electronic tongues are commented.     

Driving forces in substitution reactions of octahedral complexes: The influence of the competitive effect

The reaction of cis-[RuCl₂(P–P)(N–N)] type complexes (P–P = 1,4-bis(diphenylphosphino)butane or (1,1′-diphenylphosphino)ferrocene; N–N = 2,2′-bipyridine or 1,10-phenantroline) with monodentate ligands (L), such as 4-methylpyridine, 4-phenylpyridine and benzonitrile forms [RuCl(L)(P–P)(N–N)]⁺ species. Upon characterization of the isolated compounds by elemental analysis, ³¹P{¹H} NMR and X-ray crystallography it was found out that the type of the L ligand determines its position in relation to the phosphorus atom. While pyridine derivatives like 4-methylpyridine and 4-phenylpyridine coordinate trans to the phosphorus atom, the benzonitrile ligand (bzCN), a good π acceptor, coordinates trans to the nitrogen atom. A ³¹P{¹H} NMR experiment following the reaction of the precursor cis-[RuCl₂(dppb)(phen)] with the benzonitrile ligand shows that the final position of the entering ligand in the complex is better defined as a consequence of the competitive effect between the phosphorus atom and the cyano-group from the benzonitrile moiety and not by the trans effect. In this case, the benzonitrile group is stabilized trans to one of the nitrogen atoms of the N–N ligand. A differential pulse voltammetry experiment confirms this statement. In both experiments the [RuCl(bzCN)(dppb)(phen)]PF₆ species with the bzCN ligand positioned trans to a phosphorus atom of the dppb ligand was detected as an intermediate complex.     

Dissolving Hydroxyolite: A DNA Molecule into Its Hydroxyapatite Mold

In spite of the clinical importance of hydroxyapatite (HAp), the mechanism that controls its dissolution in acidic environments remains unclear. Knowledge of such a process is highly desirable to provide better understanding of different pathologies, as for example osteoporosis, and of the HAp potential as vehicle for gene delivery to replace damaged DNA. In this work, the mechanism of dissolution in acid conditions of HAp nanoparticles encapsulating double‐stranded DNA has been investigated at the atomistic level using computer simulations. For this purpose, four consecutive (multi‐step) molecular dynamics simulations, involving different temperatures and proton transfer processes, have been carried out. Results are consistent with a polynuclear decalcification mechanism in which proton transfer processes, from the surface to the internal regions of the particle, play a crucial role. In addition, the DNA remains protected by the mineral mold and transferred proton from both temperature and chemicals. These results, which indicate that biomineralization imparts very effective protection to DNA, also have important implications in other biomedical fields, as for example in the design of artificial bones or in the fight against osteoporosis by promoting the fixation of Ca²⁺ ions.     

Electronic tongues in flow analysis

This review presents the evolution of recent flow-based analytical systems, characterized by the use of arrays of sensors as a detection scheme. For the proper processing of the complex responses generated, the systems require the use of advanced chemometric treatment, in which received the term “electronic tongue”. Applications employing the flow injection analysis (FIA) and sequential injection analysis (SIA) are described. Chronologically, the progresses made by different research groups are shown, emphasizing their final applications in real problem solving.     

Sensitive stripping voltammetry of heavy metals by using a composite sensor based on a built-in bismuth precursor

A new graphite-epoxy composite electrode (GECE) containing Bi(NO(3))(3) as a built-in bismuth precursor for simultaneous and individual anodic stripping analysis of heavy trace metals like lead and cadmium is reported. The developed Bi(NO(3))(3)-GECE is compatible with bismuth film electrodes reported previously including the composite electrodes (Bi-GECE) recently reported by our group. Bi(NO(3))(3)-GECE displays the ability for the detection of both individual and simultaneous determination of heavy trace metals and exhibits well defined, reproducible and sharp stripping signals. The sensitive response is combined with the minimal toxicity of Bi(NO(3))(3). This novel sensor would be an appropriate alternative tool to sensors using bismuth in solution during their utilization in environmental quality monitoring as well as other applications.     

Sequential injection system with higher dimensional electrochemical sensor signals Part 2. Potentiometric e-tongue for the determination of alkaline ions

An intelligent, automatic system based on an array of non-specific-response chemical sensors was developed. As a great amount of information is required for its correct modelling, we propose a system generating it itself. The sequential injection analysis (SIA) technique was chosen as it enables the processes of training, calibration, validation and operation to be automated simply. Detection was carried out using an array of potentiometric sensors based on PVC membranes of different selectivity. The diluted standard solutions needed for system learning and response modelling are automatically prepared from more concentrated standards. The electrodes used were characterised with respect to one and two analytes, by means of high-dimensionality calibrations, and the response surface of each was represented; this characterisation enabled an interference study of great practical utility. The combined response was modelled by means of artificial neural networks (ANNs), and thus it was possible to obtain an automated electronic tongue based on SIA. In order to identify the ANN which provided the best model of the electrode responses, some of the network's parameters were optimised and its usefulness in determining NH₄⁺, K⁺ and Na⁺ ions in synthetic samples was then tested. Finally, it was used to determine these ions in commercial fertilisers, the obtained results being compared with reference methods.