Organotransition-Metal-Mediated Borane-Cage Expansion

Attempts were made to synthesize dinuclear Group 6 metal complexes of the arachno -octahydrotriborate anion. Specifically, the dimer [CpW(CO) 3 ] 2 (Cp = m 5 -C 5 H 5 ) was employed as the metal reagent. However, the formation of dinuclear metallaborane complexes did not ensue. Rather, clean, rapid, systematic borane-cage expansion was observed. The [B 3 H 8 ] m cluster was quantitatively converted to B 5 H 9 ,[B 9 H 14 ] m , or [B 11 H 14 ] m , or both, depending on reaction conditions. Refluxing a 1:1 mixture of [B 3 H 8 ] m and [CpW(CO) 3 ] 2 in toluene or dioxane lead to the rapid, quantitative conversion of [B 3 H 8 ] m to B 5 H 9 . However, refluxing a 2:1 mixture of [B 3 H 8 ] m and [CpW(CO) 3 ] 2 in the same solvents yielded [B 9 H 14 ] m and [B 11 H 14 ] m as the primary products; when glyme was the solvent, only [B 9 H 14 ] m was observed, even after prolonged heating.     

STUDIES IN THE HETEROCYCLIC COMPOUNDS V1. SOME REACTIONS OF 5-CHLORO-2-THIOPHENESULFONYL DERIVATIVES

Abstract

The reactions of 5-chloro-2-thiophenesulfonyl chloride are described. Treatment of the sulfonyl chloride with ammonia, hydrazine hydrate, sodium azide, indole and imidazole gave the sulfonamides (5), sulfonohydrazide (4), sulfonyl azide (3), 1-(5-chloro-2-thiophenesulfonyl)indole (27) and 1-(5-chloro-2-thiophenesulfonyl)-imidazole (26), respectively. The sulfonyl chloride was reacted further with 20 aryl-and cycloalkyl-amines to give the corresponding sulfonamides (6)-(25). Attempted chlorination of the sulfonyl chloride (2) with sulfuryl chloride or bromination of the sulfonyl azide (3) with pyridinium bromide perbromide failed. However, nitration of the sulfonyl chloride (2) with fuming nitric acid gave the 4-nitro-sulfonyl chloride (28), which with sodium azide afforded the 5-chloro-4-nitro-sulfonyl azide (29). The sulfonyl azides, (3) and (29), have been reacted with triphenylphosphine, triethylphosphite, norbornene and cyclohexene. The azides reacted further with indole and 1-methylindole to give the 2-sulfonyl-iminoindolines (34)-(36). The infra-red spectra and mass spectra of some of the substituted thiophenesulfonyl derivatives are discussed.     

STUDIES OF HETEROCYCLIC COMPOUNDS: VI1 THE MASS SPECTRA OF SOME 2-THIOPHENEMERCURIC DERIVATIVES

Abstract

The mass spectra of some 2-thiophenemercuric derivatives are determined and the fragmentation interpretations are based on mechanistic analogy and supported in some cases by metastable peaks and low energy mass spectra. They all fragment ultimately to the 2-thienyl cation formed either through a two-step process, by cleavage of Hg[sbnd]X bond to give the 2-thienylmercuric cation, followed by extrusion of mercury, or by a one-step process through cleavage of carbon-mercury bond. Their base peaks being the C₃H₃ ⁺ion (m/e 39).     

Molecular Recognition of Acetylaminofluorene-and Aminofluorene-modified Guanosine

Abstract

New receptors based upon a carboxamidonaphthyridine unit derivatized with the polyaromatic segments [4-(1-pyrenyl)butyroylamino] and [3-(9-anthracenyl)propanoylamino] have been synthesized and studied by ¹H NMR titration in their binding interaction to the guanosine-C8 adducts from the carcinogens 2-acetylaminofluorene and 2-aminofluorene. The high binding energy, in comparison with that of the non-derivatized analogues, is rationalized in terms of a bi-site interaction (hydrogen bonding and aromatic stacking). Although many factors may contribute to the strength of the host-guest complexes described herein, it appears that in some cases π-π interaction may induce a concomitant bending in the hydrogen bond system.     

Perylene-based profluorescent nitroxides for the rapid monitoring of polyester degradation upon weathering: An assessment

A profluorescent nitroxide possessing an isoindoline nitroxide moiety linked to a perylene fluorophore was developed to monitor radical mediated degradation of melamine-formaldehyde crosslinked polyester coil coatings in an industry standard accelerated weathering tester. Trapping of polyester-derived radicals (most likely C-radicals) that are generated during polymer degradation leads to fluorescent closed-shell alkoxy amines, which was used to obtain time-dependent degradation profiles to assess the relative stability of different polyesters towards weathering. The nitroxide probe couples excellent thermal stability and satisfactory photostability with high sensitivity and enables detection of free radical damage in polyesters under conditions that mimic exposure to the environment on a time scale of hours rather than months or years required by other testing methods. There are indications that the profluorescent nitroxide undergoes partial photo-degradation in the absence of polymer-derived radicals. Unexpectedly, it was also found that UV-induced fragmentation of the NO–C bond in closed-shell alkoxy amines leads to regeneration of the profluorescent nitroxide and the respective C-radical. The maximum fluorescence intensity that could be achieved with a given probe concentration is therefore not only determined by the amount of polyester radicals formed during accelerated weathering, but also by the light-driven side reactions of the profluorescent nitroxide and the corresponding alkoxy amine radical trapping products. Studies to determine the optimum probe concentration in the polymer matrix revealed that aggregation and re-absorption effects lowered the fluorescence intensity at higher concentrations of the profluorescent nitroxide, but too low probe concentrations, where these effects would be avoided, were not sufficient to trap the amount of polyester radicals formed upon weathering. The optimized experimental conditions were used to assess the impact of temperature and UV irradiance on polymer degradation during accelerated weathering.     

Deuterodehalogenation—a mild method for synthesising deuterated heterocycles

We report a mild and efficient method for introducing deuterium into a range of heterocycles by reacting readily available halide analogues in a deuterodehalogenation reaction using D₈-IPA or Et₃SiD under palladium-catalysed conditions.     

Hybrid phospholipid bilayer coatings for separations of cationic proteins in capillary zone electrophoresis

Protein separations in CZE suffer from nonspecific adsorption of analytes to the capillary surface. Semipermanent phospholipid bilayers have been used to minimize adsorption, but must be regenerated regularly to ensure reproducibility. We investigated the formation, characterization, and use of hybrid phospholipid bilayers (HPBs) as more stable biosurfactant capillary coatings for CZE protein separations. HPBs are formed by covalently modifying a support with a hydrophobic monolayer onto which a self‐assembled lipid monolayer is deposited. Monolayers prepared in capillaries using 3‐cyanopropyldimethylchlorosilane (CPDCS) or n‐octyldimethylchlorosilane (ODCS) yielded hydrophobic surfaces with lowered surface free energies of 6.0 ± 0.3 or 0.2 ± 0.1 mJ m^?2, respectively, compared to 17 ± 1 mJ m^?2 for bare silica capillaries. HPBs were formed by subsequently fusing vesicles comprised of 1,2‐dilauroyl‐sn‐glycero‐3‐phosphocholine or 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine to CPDCS‐ or ODCS‐modified capillaries. The resultant HPB coatings shielded the capillary surface and yielded reduced electroosmotic mobility (1.3–1.9 × 10^?4 cm² V^?1s^?1) compared to CPDCS‐ and ODCS‐modified or bare capillaries (3.6 ± 0.2 × 10^?4 cm² V^?1s^?1, 4.8 ± 0.4 × 10^?4 cm² V^?1s^?1, and 6.0 ± 0.2 × 10^?4 cm² V^?1s^?1, respectively), with increased stability compared to phospholipid bilayer coatings. HPB‐coated capillaries yielded reproducible protein migration times (RSD ≤ 3.6%, n ≥ 6) with separation efficiencies as high as 200 000 plates/m.