Ab initio calculations of isomerization reaction of diphosphene 1-sulfide to thiadiphosphirane

Ab initio Calculations of the isomerization reaction of diphosphene 1-sulfide (2′) to thiadiphosphirane (3′) suggest that the energy barrier of the reaction in the ground state is 25 kcal/mol and that 2′ lies 21 kcal/mol above 3′, while the calculations show that there exists one local minimum on the lowest triplet energy surface.     

Preparation of a novel molecularly imprinted polymer using a water-soluble crosslinking agent

A molecularly imprinted polymer was prepared using a water-soluble crosslinking agent. An ionic complex was utilized as the assembly for the template molecule and the functional monomer, and water as porogenic solvent during preparation of the imprinted polymer. The results of chromatographic evaluations for the prepared polymer suggested that the polymer had much lower hydrophobicity compared with usual octadecyl group bonded silica or the usual molecular imprinted polymer prepared from ethyleneglycol dimethacrylate, and the selective recognition ability for template molecule in the completely aqueous condition.     

On the pauling electronegativity scales—II

From the analysis of the electrostatic potential near the core-valence boundary in an atom, it is shown that the Pauling electronegativity scale χ_p is approximately given by the formula,

where N_v is the valence electron number and f(n) is some function of the periodic number in the periodic table. It is also shown in detail that the Pauling electronegativity scale is closely related to the Wang-Parr electronegativity scale which is determined as the negative of the chemical potential in density functional theory. Correlation between the Pauling and Mulliken electronegativities is briefly discussed.     

Conductive characteristics of radical‐bearing polythiophenes using a microcomb‐shaped electrode

The electric conductivity of π‐conjugated and radical‐bearing polymers, i.e., polythiophenes bearing pendant galvinoxyl and phenoxyl radical groups, was measured using a microcomb‐shaped electrode. The electric conductivity was found to be enhanced by the radical content in the polymer. The infrared (IR) and Raman spectroscopies suggested a structural change from an aromatic form to a quinoid one in the polythiophene backbone by the phenoxyl radical generation. The effect of the pendant galvinoxyl radical's unpaired electron on the electric conductivity of the polythiophene was discussed by comparing the conductivity of a radical‐bearing polystyrene and a polythiophene mixed with low‐molecular radical molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

Molecular structures of endo[4+2]π and exo[6+4]π cycloadducts via cycloaddition reaction of n-ethoxycarbonylazepine with 2,5-dimethoxycarbonyl-3,4-diphenylcyclopentadienone

The cycloaddition reaction of N-ethoxycarbonyl-1H-azepine with 2,5-dimethoxycarbonyl-3,4-diphenylcyclopentadienone gave anti-endo [4+2]π and exo [6+4]π cycloadducts. These structures were fully identified by X-ray crystallographic techniques. Mechanism for their cycloaddition reactions are also discussed.     

Template-directed dynamic synthesis of mechanically interlocked dendrimers

The versatility and efficiency of dynamic covalent chemistry (DCC) has been exploited in the convergent synthesis of mechanically interlocked dendrimers that are based upon the mutual recognition expressed between secondary dialkylammonium ions and crown ether-like macrocycles. Reversible imine bond formation is employed to clip two acyclic fragments, one of them a diformylpyridine unit bearing a dendritic side chain, and the other a complementary dianiline in the shape of the di(o-aminophenyl)ether of tetraethylene glycol, around each arm of a tritopic trisammonium ion core, thereby affording a branched [4]rotaxane. This template-directed strategy has been demonstrated to work in very high yields (>90%) with successive generations (G0-G2) of a modified Fréchet-type dendritic wedge attached to the 4-position of the diformylpyridine unit. Reduction of these dynamic dendritic systems is achieved upon treatment with borane.THF and results in kinetically stable compounds. The inherent modularity of the overall process should allow for the rapid and straightforward access to many other analogous mechanically interlocked systems in which either the branched core or the dendritic periphery can be modified to suit the needs of any given application of these molecules. Indeed, the dynamic nature of the initial thermodynamically mediated assembly could be utilized in order to amplify particular products from a potential library as a result of a selective recognition process.     

Dynamic capillary coatings with zwitterionic surfactants for capillary isoelectric focusing

The use of surfactants as additives was demonstrated for the first time in capillary isoelectric focusing (CIEF) to dynamically modify the surfaces of bare fused silica capillaries. These surfactants were zwitterionic sulfobetaines: dodecyldimethyl (3-sulfopropyl) ammonium hydroxide (C12N3SO3), hexadecyldimethyl (3-sulfopropyl) ammonium hydroxide (C16N3SO3) and coco (amidopropyl)hydroxyldimethylsulfobetaine (Rewoteric AM CAS U). They were added directly to the protein-ampholyte mixture, and remained in the capillary during isoelectric focusing and mobilization. The C16N3SO3 and CAS U coatings were shown effective in CEF. Separation of seven IEF protein standards was obtained, with significantly improved resolution compared to that from an uncoated silica capillary. The effect of these surfactants on the electroosmotic flow (EOF) in CIEF was determined. CAS U was effective in suppressing the EOF at neutral and alkaline pH conditions, C16N3SO3 was effective in suppressing EOF at acidic and neutral pH conditions. C12N3SO3 however had little effect on the EOF. The pH gradients formed inside these surfactant coated capillaries were recta-linear at pH 6 to 9 (R2 approximately equal to 0.99). Reproducibility of migration time and peak area was determined. For all three coatings, the migration time standard deviations were less than 1.6 min, and the relative standard deviations of area were below 10%. The protein recovery in the CAS U-modified capillary was quantitative or near-quantitative for five of the seven proteins studied.     

Interpretation of structure formation during the sol-gel transition of a resorcinol-formaldehyde solution by population balance

Growth of colloidal particles formed during the sol-gel transition of a resorcinol-formaldehyde (RF) solution was simulated based on the population balance equation by using the discrete-sectional model (DSM). During the early stage of the sol-gel transition, the transient change of sizes of colloidal particles estimated by this method agreed well with the previous experimental observation by dynamic light scattering (DLS), which confirmed the influence of the catalyst concentration of a starting RF solution on the growth rate of the particles. From the size distribution of colloidal particles predicted at the gelation time, the surface area of a RF hydrogel after the completion of the sol-gel transition was estimated, which coincided with the BET surface area of a RF aerogel because the porous structure of a hydrogel was maintained and few micropores were formed during supercritical drying.     

Non empirical quantum mechanical calculations of the1H,13C,15N and17O magnetic shielding constants and of the spin-spin coupling constants in formamide,hydrated formamide and N-methylformamide

The magnetic shielding constants of the different atoms of formamide, hydrated formamide and N-methylformamide are calculated by anab initio method. For the protons of formamide the measured differences between their chemical shifts are correctly reproduced by theory, provided that the molecular geometry used as input is carefully chosen. The differences between the values of the magnetic shielding constants calculated for formamide and hydrated formamide show that intermolecular hydrogen bonding produces variations of chemical shifts for all the atoms of the molecule except the formyl proton. The calculated chemical shift variations between formamide and N-methylformamide are compared to the experimental values and discussed in relation with different hydrogen bonding possibilities of the two molecules. The calculation of the contact term of the spin-spin coupling constants of formamide and hydrated formamide shows that in most cases the measured trends are satisfactorily reproduced and that the variations of these terms upon hydration are less than 3%.