Theoretical interpretation of the linear relationship between the hyperfine-structure constants in molecules and their radicals

The hyperfine-interaction constants of a number of radicals (A _H and ) and molecules (J _HH and {ie590-02}) were calculated within the framework of the semiempirical MO LCAO method. It is shown that there is a linear correlation between the atom-atom polarizabilities _rs which determine the values of the J constants and the spin densities in the corresponding radicals.     

Interactions between free radicals and a graphene fragment: physical versus chemical bonding, charge transfer, and deformation

The adsorption of six free radicals (FRs) respectively on a graphene fragment was studied using a density functional tight‐binding method with the inclusion of an empirical dispersion term in total energy. The results indicate that the different interaction paths between the FRs and the graphene lead to different forms of physical (PA) or chemical adsorptions (CA). The CA appears only in the condition where some of the nonhydrogen atoms are closer to the graphene, with the deformation occurring in the latter. The charge transfer increases with the increase in adsorption energy in every FR‐graphene system. Although the deformation in the graphene is negligible in all PA cases, the FR is closer to the graphene and the graphene deformation is clearer in all CA cases, with all atomic displacements being larger than 0.1 Å. Our findings are useful not only for FR scavenging but also for studying the interaction between general molecules and material surfaces. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Polymer science with transition metals and main group elements: Towards functional,supramolecular inorganic polymeric materials

Inorganic polymers are relatively unexplored because the efficient formation of macromolecular chains from atoms of transition metals and main group elements has presented a synthetic challenge. Nevertheless, these materials offer exciting opportunities for accessing properties that are significantly different from and which therefore complement those available with the well‐established organic systems. Inorganic block copolymers are of particular interest for the generation of functional, nanoscale supramolecular architectures and hierarchical assemblies using self‐assembly processes. This article focuses on research in my group over the past decade, which has targeted the development of new and controlled routes to inorganic polymers and their subsequent use in forming supramolecular materials as well as studies of their properties and applications. The use of ring‐opening polymerization (ROP) and transition‐metal‐catalyzed polycondensation approaches are illustrated. Controlled ROP procedures have been developed that allow access to polyferrocene block copolymers that self‐assemble into interesting nanoscopic architectures such as cylinders and superstructures such as flowers. The future prospects for inorganic polymer science are discussed, and a growing emphasis on the study of supramolecular inorganic polymeric materials is predicted. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 179–191, 2002     

1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines: synthesis, photophysical properties, and observation of a linear correlation between the fluorescent wavelength and Hammett substituent constants

1-Alkynyl- and 1-alkenyl-3-arylimidazo[1,5-a]pyridines were synthesized. The Sonogashira coupling of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various terminal alkynes with Pd(PPh(3))(2)Cl(2) (10 mol %) and CuI (10 mol %) in triethylamine at 80 °C for 12 h afforded the corresponding 1-alkenyl-3-arylimidazo[1,5-a]pyridines in good to excellent yields. The Mizoroki-Heck reaction of 3-aryl-1-iodoimidazo[1,5-a]pyridines and various styrene derivatives proceeded smoothly with Pd(OAc)(2) (5 mol %), IMes·HCl (10 mol %), and Cs(2)CO(3) (2 equiv) in DMA at 130 °C for 20 h to give the alkenylated imidazo[1,5-a]pyridines in moderate to high yields. The fluorescence maxima and fluorescence quantum yields of the alkynylated products were 458-560 nm and Φ(F) = 0.08-0.26 in chloroform solution, and those of the alkenylated imidazopyridines were 479-537 nm and Φ(F) = 0.03-0.13. The absorption behaviors of the obtained alkynylated and alkenylated imidazo[1,5-a]pyridines showed a good fit to the values predicted by TDDFT calculations at the B3LYP/6-311++G(d,p) level. In addition, the alkynylated imidazo[1,5-a]pyridines obtained showed linear correlations between the Hammett substituent constants of the substituents on the arylalkynyl group and their fluorescence wavelengths.     

Infrared spectra and structures of carbanions—XI: Estimation of σ+ constants of anionic substituents

σ⁺ constants of H₂Cxxx- (?11.2), HNxxx- (?7.6), C₂H₅OOC-HCxxx- (?5.0), NC-HCxxx- (?5.4) and some other anionic substituents were estimated on the basis of ν_CN of the corresponding benzonitrile anions and by using the correlations $\text{ν}{}_{\mathrm{<mtext>CN</mtext>}}\text{σ}{}^{\mathrm{+}}$ for benzonitriles, in polar aprotic solvents.     

Occlusion of grubbs' catalysts in active membranes of polydimethylsiloxane: catalysis in water and new functional group selectivities

The Grubbs' first and second generation catalysts were occluded into cross-linked slabs of polydimethylsiloxane with volumes from 1 mm3 to 1 cm3 by swelling the polymer with catalyst and methylene chloride. Methylene chloride was evaporated under vacuum to yield occluded catalysts where their solvent was polydimethylsiloxane. These occluded catalysts were reacted with alkenes dissolved in H2O or H2O/MeOH mixtures that diffused into the polydimethylsiloxane to react by ring-closing metathesis and cross metathesis. Control experiments revealed that the catalysts remained occluded and metathesis did not occur in the solvent. Occlusion of these catalysts allowed commercially available Grubbs' catalysts to be used with H2O as the solvent while isolating the H2O sensitive ruthenium methylidene from exposure to H2O. Functional group selective experiments were carried out where the polydimethylsiloxane was an "active" membrane to exclude salts. Polydimethylsiloxane is a hydrophobic polymer, so the deprotonated salt of diallylmalonic acid did not diffuse into it while a diallylether diffused into it and reacted by metathesis. Thus, by controlling the polarity of reagents their reactivity can be controlled owing to the properties of polydimethylsiloxane rather than those of the Grubbs' catalysts. Occlusion of catalysts in polydimethylsiloxane has been shown to add new selectivities to mature catalysts.     

Rate and equilibrium constants of transfer of the dimethylcarbamoyl group between substituted pyridines and their N-oxides

Transfer of the dimethylcarbamoyl group from N-acyloxypyridinium salts to pyridines and from N-acylpyridinium salts to pyridine N-oxides was studied in acetonitrile. Equations relating the reaction rates and equilibria in the N-O and O-N acyl transfer series to the basicity of the nucleophile and leaving group were obtained. The reactions all are one-stage and occur by the forced concerted SN2 mechanism. The intersecting state model was used to obtain a modified Marcus equation that accounts for the asymmetry of the transition state with respect to reagents and products and allows uncontradictory analysis of the reaction mechanism.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1720–1727.Original Russian Text Copyright © 2004 by Rybachenko, Shreder, Gokhfeld, Chotii, Kovalenko, Lenska.This revised version was published online in April 2005 with a corrected cover date.     

Towards functional nanostructures: Ionic self-assembly of polyoxometalates and surfactants

Major recent advances in the field of POM-surfactant ISA complexes are the extension of the studies into both thermo- and lyotropic phase behaviour, and the use of the vesicle motif for the production of novel hybrid vesicle structures. The use of metal-coordinating functional surfactants has led to the expression of synergistic functionality in POM-based materials.     

Diastereoselectivity controlled by electrostatic repulsion between the negative charge on a trifluoromethyl group and that on aromatic rings

Intramolecular electrostatic repulsions between the local negative charge on a trifluoromethyl group and that on the ortho position of an aryl moiety of a nucleophile was found to be a controlling factor of the diastereoselectivity in a cyclopropanation reaction, in which the electrostatic repulsion was evaluated quantitatively.     

Exciton diffusion and interfacial charge separation in meso-tetraphenylporphyrin/TiO2 bilayers: effect of ethyl substituents

The photoinduced charge separation efficiency in porphyrin/TiO2 bilayers has been determined using the time-resolved microwave conductivity (TRMC) technique. Porphyrins investigated are unsubstituted meso-tetraphenylporphyrin (TPP) and meso-tetra(4-ethylphenyl)porphyrin (TEPP). TEPP/TiO2 bilayers exhibit a charge separation efficiency per incident photon at the Soret band maximum of 6.2%, which is considerably higher than the efficiency of 1.2% found for TPP/TiO2 bilayers. Exciton diffusion lengths of 7 A for TPP and 75 A for TEPP are obtained from fitting a model for the charge separation efficiency to the experimental data. Optical measurements on the porphyrin derivatives on quartz yield a 20 times higher fluorescence quantum yield and a 7 times higher fluorescence rate constant for TEPP layers as compared to TPP layers. The exciton lifetime of 800 ps found for TEPP layers is considerably longer than the lifetime of 260 ps in TPP layers. The exciton diffusion coefficients, determined from the exciton diffusion length and the exciton lifetime, are found to be 2.10(-9) m(2)/s for TPP and 7.10(-8) m(2)/s for TEPP. The difference is discussed in terms of the presence of face-to-face dimers or larger aggregates in TPP layers.     

Determining partition constants of polar organic molecules between the oil/interfacial and water/interfacial regions in emulsions: a combined electrochemical and spectrometric method

We have developed a new approach for estimating distributions of polar additives in opaque, surfactant based, macroemulsions based on the pseudophase model for homogeneous micellar and microemulsion solutions. The distribution of a polar additive, such as an antioxidant, AO, within emulsions is expressed in terms of two partition constants, one between the oil and interfacial regions, P(O)I, and the other between the water and interfacial regions, P(W)I. To estimate values for P(O)I and P(W)I requires fitting two independent data sets with two independent mathematical relations and solving equations simultaneously for the two parameters. The experimental protocols were developed for determining the partition constants of tertbutylhydroquinone, TBHQ, in a stirred emulsion composed of octane, dilute aqueous acid, and hexaethyleneglycol monododecyl ether, C12E6. One data set was obtained by electrochemical determination of the observed rate constant, k(obs), for reaction of TBHQ with an arenediazonium ion probe as a function of C12E6 volume fraction. The second data set was obtained by determining the partition constant, P(O)W, of TBHQ between octane and water in the absence of surfactant by UV-visible spectrometry. TBHQ is almost 30 times more soluble in water than octane: P(O)W = 27.5. The values of the partition constants in the emulsion are P(O)I = 1.84 x 10(4) and P(W)I = 6.73 x 10(2). The partition constants were used to estimate the fraction of TBHQ in each region; for example, 96% of the TBHQ is located in the interfacial region at 0.02 volume fraction of C12E6. Our approach is quite general and should be applicable to any polar organic compound that reacts with the arenediazonium ion probe in emulsions composed of virtually any type of oil and surfactant. Comparisons of the rate constants for reaction of the antioxidant in the interfacial region of the emulsion, which can be obtained from the electrochemical results, may lead to a scale of antioxidant efficiency that is independent of the distribution of the antioxidant in the emulsion.     

Differential scanning potentiometry: surface charge development and apparent dissociation constants of natural humic acids

Humic acids (HA) are the main components of soil organic matter which can form complexes with metal ions and other soil and/or water contaminants. Here, we focus on their acid-base properties. HA were extracted from two different soils (Tipic Ustifluvent and Entic Haplustoll) with different vegetation. In this study we use a simple method, differential scanning potentiometry (DSP), to determine HA buffer capacity distribution, apparent dissociation constant values and surface charge development.     

Electrodeposition of monodispersed metal nanoparticles in a nafion film: Towards highly active nanocatalysts

We have explored a new and facile method for the fabrication of metal nanoparticles on the electrode surface. The approach for fabricating metal nanoparticles was carried out by two steps consisting of ion-exchange in nafion film coated on the electrode and subsequent reduction of metal ions to metallic nanoparticles by electrochemical method. The results of characterization by TEM show that metal nanoparticles were nearly monodispersed in the whole nafion film. The average diameters of Cu, Co and Ni nanoparticles were statistically measured to be 5.1 nm ± 0.2 nm, 4.6 nm ± 0.2 nm and 4.7 nm ± 0.2 nm, respectively. The amount of metal nanoparticles can be readily controlled by the amount of nafion coated on the electrode. By performing the H₂O₂ reduction at the obtained Cu nanoparticles, the high electrocatalytic activity of metal nanoparticles fabricated has been confirmed.