The synthesis of a pyrrole-functionalized cyclobis(paraquat-p-phenylene) derivative and its corresponding [2]rotaxane and [2]catenane and their subsequent deposition onto an electrode surface

We report the convenient synthesis of a pyrrole-functionalized tetracationic cyclophane, [2]rotaxane, and [2]catenane. X-ray crystallography has confirmed the interlocked structure of the catenane. We have investigated the solution properties of these systems using solution electrochemistry, NMR, and UV-vis spectroscopy. We have also demonstrated that it is possible to immobilize these systems onto a platinum working electrode surface. We have shown that films of the cyclophane have the ability to undergo complexation with a dialkyloxynaphthalene derivative.     

Kinetic investigation of small systems using different algorithms

We have investigated different algorithms for the simulation of kinetics of small systems. We have simulated the first order reversible reaction with the Gillespie, Gibson and Bruck time simulation as a function of Poisson distribution and compared the results of three algorithms. We have also simulated intracellular viral kinetics for a genome with Gillespie and Poisson distribution algorithms.     

Electrical transport properties of semiconducting lithium molybdate glass nanocomposites

We have reported the formation of lithium molybdate glass nanocomposites embedded with lithium molybdate nanophases from the x-ray diffraction and transmission electron microscopic studies. We have investigated the dc electrical conductivity in a wide temperature range for these glass nanocomposites, which exhibit semiconducting behavior. We have analyzed the dc electrical data in the light of polaronic conduction models of Mott and Schnakenberg. We have also studied ac electrical conductivity of these glass nanocomposites in wide temperature and frequency ranges. The experimental ac results have been analyzed with reference to various theoretical models based on quantum-mechanical tunneling and hopping over the barrier. We have observed that the temperature dependence of the dc conductivity is consistent with the polaronic hopping models, while the temperature and frequency dependence of the ac conductivity is consistent with the polaronic tunneling models.     

Energetics and metastability of the adenine dication observed in proton-adenine collisions

We present here a study that deals with the correlated fragmentation of a doubly charged adenine molecular target induced by a 100 keV proton beam. We have elucidated part of the dissociation dynamics for several channels and have obtained the corresponding kinetic energy released values. We have extracted activation energies by combining our experimental data with computations using the ab initio GAMESS code. We have observed metastability patterns against fragmentation, for which we have extracted the temporal mechanism (one or two steps). Subsequently, we have obtained lifetimes in the 100-200 ns range. In the simplest case of two-body fragmentation with the emission of mass 28, the determination of transition states and reaction paths has showed that emission of the H-C-N-H fragment is preferred to that of C-N-H(2). From the calculated activation barriers and lifetimes, we have deduced an equivalent temperature of the dication that we have compared with the existing models.     

Approximate additivity of anion-pi interactions: an ab initio study on anion-pi, anion-pi(2) and anion-pi(3) complexes

We have studied the additivity of the anion-pi interaction using high level ab initio calculations. We have optimized chloride and bromide complexes with one, two and three aromatic units (such as trifluoro-s-triazine and s-triazine). We have analyzed the interaction using the atoms in molecules theory and studied the charge transfer using several methods for deriving atomic charges. The results revealed additivities of both the geometries and the binding energies. We have also proposed a neutral receptor for chloride based on multiple anion-pi interactions. Finally, we have simulated solvent effects within the self-consistent reaction field model.     

Volumetric and infrared measurements on amorphous ice structure

We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous.     

Proton transference in hydrogen bonded systems. I. Uracil tautomerism

We have made a detailed analysis of the adequacy of different theoretical approaches to the study of uracil tautomerism. We have considered the effect of molecular relaxation and the ability of several methods to reproduce it. We have also considered their performance in predicting the tautomerization energy barrier. We found that semiempirical methods are not adequate for predicting the energy value but that they can be used for obtaining geometry optimizations. We also found a strong discrepancy between the energy values predicted by a minimal basis set and a 2ζ basis set, the last one being 24.9 kcal/mol. The implications of these findings are discussed and the results compared with experimental evidence.     

Effect of External Acidity of Mordenite-Supported Catalysts on the 2,2-Dimethylbutane Content in Hydroisomerization Products of n-Hexane

We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.     

Molecular dynamics comparative study of methane–nitrogen and methane–nitrogen–ethane systems

This work concerns the site–site interaction study of 256 particles using the Buckingham potential model. We have calculated the new parameters of the Buckingham potential using an iterative algorithm with a mean square method. This adapted model allows determining the characteristics for each state point. We have applied this model to study the liquefied natural gas LNG properties for methane-nitrogen and methane–nitrogen–ethane mixtures by molecular dynamics. We have calculated the thermodynamic, dynamic and structural properties for both the microcanonical NVT and the isothermal-isobaric NPT ensembles of binary and ternary systems from the SP₁ to SP₉ points. Then, we have compared the results between binary and ternary systems. We have obtained a good prediction on transport properties. From the calculated values of self-diffusion coefficient and viscosity, we have confirmed the liquid state of the liquefied natural gas LNG system.     

Transient electric birefringence of wormlike macromolecules in electric fields of arbitrary strength: a computer simulation study

We have studied the birefringence decay of linear models of macromolecules for two different types of flexibility, the broken-rod chain and the wormlike chain, using a computer simulation of a transient electric birefringence experiment. We have paid particular attention to the influence of the intensity of the orienting field, including two orienting mechanisms, the induced dipole, and the permanent dipole. We have compared wormlike and broken-rod models of the same radius of gyration, finding that they present a different decay curve under the influence of the same intensity of the field. We have seen that these differences are due to the faster relaxation times (smaller in the wormlike chain model) and amplitudes, because, regardless of the type of flexibility, the overall size of a molecule (measured by the radius of gyration) essentially determines the longest relaxation time. We have also analyzed how the relaxation process is affected by the degree of flexibility, the orientation mechanisms, and the intensity of the field. Studying a different aspect, we have paid attention to the deformation of a molecule in a transient electric birefringence experiment as a source of information. In this work we have developed equations to characterize this deformation in terms of one of the components of the gyration tensor, if a dynamic light scattering experiment under the influence of an electric field could be performed. To develop this work we have simulated the Brownian dynamics of the different models, relaxing after the removal of an orienting external electric field of arbitrary strength. A comparison with other methods such a the rigid body treatment or the correlation analysis of Brownian trajectories has also been included. We have seen that differences between the two Brownian dynamics methods are small and that the rigid-body treatment is only an acceptable approximation to obtain the longest relaxation time.     

Size-dependent properties of Zn(m)S(n) clusters: a density-functional tight-binding study

We present the results of our theoretical calculations on structural and electronic properties of ligand-free Zn(n)S(n) [with n ranging from 4 to 104 (0.8-2.0-nm diameter)] clusters as a function of size of the clusters. We have optimized the structure whereby our initial structures are spherical parts of either zinc-blende or wurtzite structure. We have also considered some hollow bubblelike structures. The calculations are performed by using a parametrized linear combination of atomic orbitals-density-functional theory-local-density approximation-tight-binding method. We have focused on the variation of radial distribution function, Mulliken populations, electronic energy levels, band gap, and stability as a function of size for both zinc-blende and wurtzite-derived ZnS clusters. We have also reported the results of some nonstoichiometric Zn(m)S(n) (with m+n=47, 99, 177) clusters of zinc-blende modification.     

Synthesis of Quinoline-8-selenol, Its Complex Compounds with Metals and Their Cytotoxic Activity

We have developed a novel method for synthesis of quinoline-8-selenol using selenourea instead of the previously used potassium selenocyanate. We have synthesized a series of metal quinoline-8-selenolates. We have studied the cytotoxic activity of the synthesized compounds against HT-1080, MG-22A, B16, Neuro 2A tumor cells. Mercury quinoline-8-selenolate is distinguished by high cytotoxicity for the three cell lines; the cadmium complex is most effective against B16 melanoma cells.     

Etude des dimensions moleculaires des polymeres dissous dans des melanges binaires de solvants polaires et non polaires—I. Polyvinyl-2 pyridine

We have studied the molecular dimensions of poly-2-vinylpyridine in solution in binary solvent mixtures consisting of a non polar and a polar component, viz. benzene-ethanol and benzene-chloroform. We have also studied the preferential solvation of the same polymer in the above mixtures using light scattering. We have observed a conformational transition of P2VP taking place in a composition region for each solvent mixture. This transition shows as a discontinuity in the unperturbed dimensions, in the long range interactions parameter and in the parameter of preferential solvation of the polymer. We think that this transition is related to the existence of two ordered structures of the polymer chain, one stable before and the other after the transition region.     

Catalytic, asymmetric alpha-chlorination of acid halides

We present a full account of a tandem catalytic, asymmetric chlorination/esterification process that produces highly optically enriched alpha-chloroesters from inexpensive, commercially available acid halides using cinchona alkaloid derivatives as catalysts and polychlorinated quinones as halogenating agents. We have performed kinetics and control experiments to investigate the reaction mechanism and establish conditions under which the reactions can be best performed. We have developed NaH and NaHCO3 shuttle base systems as the easiest and most cost-effective ways of conducting the reactions, rendering the methodology economically competitive with known chiral halogenation procedures. We have also demonstrated the utility of our reactions by converting the products to synthetically useful derivatives.     

The synthesis of symmetrical bis-1,2,5-thiadiazole ligands

We have been engaged in a search for coordination catalysts for the copolymerization of polar monomers (such as vinyl chloride and vinyl acetate) with ethylene. We have been investigating complexes of late transition metals with heterocyclic ligands. In this report we describe the synthesis of a symmetrical bis-thiadiazole. We have characterized one of the intermediates using single crystal X-ray diffraction. Several unsuccessful approaches toward 1 are also described, which shed light on some of the unique chemistry of thiadiazoles.     

Kinetics of Hydroperoxide Epoxidation of 1-Octene in the Presence of MoB2

We have studied the kinetics of the process of epoxidation of 1-octene by tert-butyl hydroperoxide in the presence of molybdenum boride MoB₂. We have studied the effect of the concentrations of starting materials and reaction products on the process. We suggest a kinetic scheme and we calculate the kinetic parameters of the process.     

Stationary coupled cluster response: Role of cubic terms in molecular properties

We have demonstrated an application of a stationary coupled cluster response approach for molecular properties using an Euler functional. This involves terms which are of cubic power in cluster amplitudes. We have shown that these are important terms and have also discussed the convergence properties of the functional for higher order properties.     

Monte Carlo analyses of multiple backscattering of gamma rays

We have written a Monte Carlo code to simulate the experimental results of a previously reported study. We were able to analyse the energy distributions of photons that reached the detector system after suffering several successive Compton scatterings in the target. We have also investigated how the number of multiply backscattered events depends on the target thickness and the energy of the primary photons.     

Stimuli-responsive polyelectrolyte polymer brushes prepared via atom-transfer radical polymerization

We present an account of our research into polyelectrolyte polymer brushes that are capable of acting as stimuli-responsive films. We first detail the synthesis of poly(acrylic acid) polymer brushes using ATRP in a "grafting from" strategy. Significantly, we employed a chemical-free deprotection step that should leave the anchoring ester groups intact. We have demonstrated how these polymer assemblies respond to stimuli such as pH and electrolyte concentration. We have used poly(acrylic acid) polymer brushes for the synthesis of metallic nanoparticles and review this work. We have used XPS, ATR-FTIR, and AFM spectroscopy to show the presence of silver and palladium nanoparticles within polymer brushes. Finally, we report the synthesis of AB diblock polyampholyte polymer brushes that represent an extension of polyelectrolyte polymer brushes.     

Effect of atmospheric pressure variations on the <Superscript>222</Superscript>Rn activity concentration in the air of a wine cellar

We have measured the variation of atmospheric pressure and of ²²²Rn activity concentration in the air of a wine cellar with an AlphaGAURD type ionization chamber radon monitor. We have found that the ²²²Rn activity concentration varies inversely with pressure. To explain this behavior we have done model calculations. We have compared the results of model calculations with the results of experimental measurements, and we have found that the model is capable to reproduce some part of the variation of ²²²Rn activity concentration.