A study of the ionic liquid mediated microwave heating of organic solvents

The use of ionic liquids as aids for microwave heating of nonpolar solvents has been investigated. We show that hexane and toluene together with solvents such as THF and dioxane can be heated way above their boiling point in sealed vessels using a small quantity of an ionic liquid, thereby allowing them to be used as media for microwave-assisted chemistry. Using the appropriate ionic liquid, the heating can be performed with no contamination of the solvent. To show the applicability of the system, two test reactions have been successfully performed.     

Supramolecular effects on the dynamics of radicals in MFI zeolites: a direct EPR investigation

Photolysis of the supramolecular complexes (dibenzyl ketones@ZSM-5) produced supramolecular complexes of benzyl radicals@ZSM-5, which were directly detected by CW-EPR spectroscopy, and provided information on the dynamics of the radicals. The lifetimes of the radicals increased as the group X attached to the carbon atom at the radical center increases from X = H (t(1/2) ca. 2 min) to X = (CH(2))(4)CH(3) (t(1/2) > 200 min). In addition, line broadening of the EPR signal was observed as the group X increases. Experiments involving cation-exchanged zeolites (MZSM-5; M = Li, Na, K, Rb, Cs) showed a strong dependence of the radical lifetime on the size of the cation (t(1/2) ca. 10 min for Li and t(1/2) > 200 min for Cs). The results are discussed in terms of supramolecular steric effects on the radical-radical reactions in the zeolite supercages.     

Potent competitive inhibition of α-galactosidase and α-glucosidase activity by 1,4-dideoxy-1,4-iminopentitols: syntheses of 1,4-dideoxy-1,4-imino-d-lyxitol and of both enantiomers of 1,4-dideoxy-1,4-iminoarabinitol

The syntheses of 1,4-dideoxy-1,4-imino-D-lyxitol (3), 1,4-dideoxy-1,4-imino-d-arabinitol (4) and 1,4-dideoxy-1,4-imino-l-arabinitol (5) are reported; (3) is a potent competitive inhibitor of α-galactosidase (green coffee beans) and (4) a competitive inhibitor of α-glucosidase (Brewer's yeast) suggesting that iminopentitols have considerable potential as glycosidase inhibitors. (4) was found to be identical to an alkaloid recently isolated from $\text{Angylocalyx boutiqueanus}$.     

THE EFFECT OF ALIPHATIC ALCOHOLS ON FLUORESCENCE QUENCHING AND FLUORESCENCE POLARIZATION OF LUMINESCENCE PROBES IN HEXADECYLTRIMETHYLAMMONIUM BROMIDE MICELLES

Abstract— The fluorescence quenching of the indole chromophore by NO⁻₂ and the fluorescence depolarization of several luminescence probes in aqueous solutions containing hexadecyltrimethylammonium bromide (HDTBr) were measured as a function of added C₂–C₄ aliphatic alcohol concentration. The fluorescence decay profiles of pyrene in the micellar solutions were also measured to estimate the aggregation number of the micelles. The addition of n -butyl alcohol significantly reduces the fluorescence quenching rate and the aggregation number and increases the extent of fluorescence depolarization in HDTBr micellar systems. The addition of ethyl alcohol shows a similar but smaller effect.     

Improved preparation of h5-C5H5 Fe(CO)2(h1-alkyl) complexes from [h5-C5H5Fe(CO)2(h2-alkene)]+BF4−

Sodium cyanoborohydride has been found to be very effective for the conversion of [(h⁵-C₅H₅)Fe(CO)₂(h²-alkene)]⁺BF₄^? complexes to the corresponding h¹-alkyl derivatives.     

Aryloxy radicals from diaryloxydiazirines: alpha-cleavage of diaryloxycarbenes or excited diazirines?

The synthesis of diaryloxydiazirines, precursors to diaryloxycarbenes, is described. Thermolyses of the diazirines afford anticipated carbene products, but photolyses afford both carbenes and aryloxy radicals by alpha-scission. UV spectra of the carbenes and radicals are observed. [reaction: see text]     

Interactions between spherical colloids mediated by a liquid crystal: a molecular simulation and mesoscale study

Monte Carlo simulations and dynamic field theory (DyFT) are used to study the interactions between dilute spherical particles, dispersed in nematic and isotropic phases of a liquid crystal. A recently developed simulation method (expanded ensemble density of states) was used to determine the potential of mean force (PMF) between the two spheres as a function of their separation and size. The PMF was also calculated by a dynamic field theory that describes the evolution of the local tensor order parameter. Both methods reveal an overall attraction between the colloids in the nematic phase; in the isotropic phase, the overall attraction between the colloids is much weaker, whereas the repulsion at short range is stronger. In addition, both methods predict a new topology of the disclination lines, which arises when the particles approach each other. The theory is found to describe the results of simulations remarkably well, down to length scales comparable to the size of the molecules. At separations corresponding to the width of individual molecular layers on the particles' surface, the two methods yield different defect structures. We attribute this difference to the neglect of density inhomogeneities in the DyFT. We also investigate the effects of the size of spherical colloids on their interactions.     

Rapid cyanation of aryl iodides in water using microwave promotion

We show that using water in conjunction with microwave heating it is possible to prepare aryl nitriles from the corresponding aryl iodides rapidly and in high yield without the need for a palladium catalyst.     

Single-walled carbon nanotube combing during layer-by-layer assembly: from random adsorption to aligned composites

Oriented SWNTs in polymer composites have shown dramatic improvements in the physical properties of a composite because of the anisotropic shape and properties of SWNTs. Controlled alignment of SWNTs during composite fabrication implies better material function performance. This letter reports a new fabrication technique whereby aligned SWNTs and robust SWNT-polymer composites can be made using a fusion method of SWNT combing and layer-by-layer (LBL) assembly. As we previously reported, LBL assembly demonstrated exceptional processing ability in constructing the uniform distribution of a SWNT-polymer composite. Combined with this uniformity, this SWNT combing technique endows controlled alignment of single-stranded SWNTs in a SWNT-polymer composite system. SWNT combing employs air-water interfacial forces to change the molecular topography from the random adsorption state to the stretched alignment of SWNTs. More specifically, air-water interfacial forces are associated with an excess viscous drag force and an intrinsic dewetting rate along SWNTs. Moreover, the alignment efficiency of SWNTs is high enough to construct a multilayered LBL film with horizontal-linear weaving structures. This simple method also can be applied for aligning other nanowire materials because it utilizes simple geometric features of SWNTs.     

Odd carbon long linear chains HC2n+1H (n = 4-11): properties of the neutrals and radical anions

The optimized geometries, adiabatic electron affinities, vertical electron affinities, vertical electron detachment energies (for the anions), and IR-active vibrational frequencies have been predicted for the long linear carbon chains HC(2)(n)()(+1)H (n = 4-11). The B3LYP density functional combined with DZP and TZ2P basis sets was used in this theoretical study. These methods have been extensively calibrated versus experiment for the prediction of electron affinities (Chem. Rev. 2002, 102, 231). The computed physical properties are discussed and compared with the even carbon chains HC(2)(n)()H. The predicted electron affinities form a remarkably regular sequence: 2.12 eV (HC(9)H), 2.42 eV (HC(11)H), 2.66 eV (HC(13)H), 2.85 eV (HC(15)H), 3.01 eV (HC(17)H), 3.14 eV (HC(19)H), 3.25 eV (HC(21)H), and 3.35 eV (HC(23)H). These electron affinities are as much as 0.4 eV higher than those for analogous even carbon chains. The predicted structures display an intermediate cumulene-polyacetylene type of bonding, with the inner carbons appearing cumulenic and the outer carbons polyacetylenic.