Large melting point depression of 2–3‐nm length‐scale nanocrystals formed by the self‐assembly of an associative polymer: Telechelic,pyrene‐labeled poly(dimethylsiloxane)

Large melting point depressions for organic nanocrystals, in comparison with those of the bulk, were observed in an associative polymer: telechelic, pyrene‐labeled poly(dimethylsiloxane) (Py‐PDMS‐Py). Nanocrystals formed within nanoaggregates of pyrenyl units that were immiscible in poly(dimethylsiloxane). For 5 and 7 kg/mol Py‐PDMS‐Py, physical gels resulted, with melting points exceeding 40 °C and with small‐angle X‐ray scattering peaks indicating that the crystals were nanoconfined, were 2–3 nm long, and contained roughly 18–30 pyrenyl dye end units. In contrast, 30 kg/mol Py‐PDMS‐PY was not a gel and exhibited no scattering peak at room temperature; however, after 12 h of annealing at ?5 °C, multiple melting peaks were present at 5–30 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3470–3475, 2004     

Headspace single-drop microextration for the detection of organotin compounds

The performance of single-drop microextraction (SDME), coupled with gas chromatography/mass spectrometry, was assessed for the determination of tributyltin compounds in water and solid samples. Experimental parameters impacting the performance of SDME, such as microextraction solvent and sampling and stirring time, were investigated. Analytical results obtained by SDME were compared with those generated by conventional solid phase microextraction (SPME) and liquid-liquid extraction (LLE) for the determination of TBT in PACS-2 sediment certified reference material (CRM).     

Preparation,properties and X-ray cystal structures of complexes of 4,4-diethylmorpholinium with 2,5-dibromo- and 2,5-dichloro-7,7,8,8-tetracyano-p-quinodimethane : DEM(TCNQBr2)2 and DEM-TCNQCl2

4,4-Diethylmorpholinium forms a 1:2 complex with 2,5-dibromo-TCNQ and a 1:1 complex with 2,5-dichloro-TCNQ; both are insulators at room temperature, and their single crystal $\text{X}$-ray structures have been determined at 293 K.     

Thermal and mechanical properties of UV irradiated collagen/chitosan thin films

The thermal and mechanical properties of collagen/chitosan blends before and after UV irradiation have been investigated using thermal analysis and mechanical (Instron) techniques. Comparisons were made with the thermal and mechanical properties of both collagen and chitosan films. Air-dried collagen, chitosan and collagen/chitosan films were exposed to UV irradiation (wavelength 254 nm) for different time intervals. Thermal properties of collagen/chitosan blends depend on the composition of the blend and are not significantly altered by UV irradiation.Mechanical properties such as ultimate tensile strength and ultimate percentage of elongation were much better for collagen films than for collagen/chitosan films. The results have shown that the mechanical properties of the blends were greatly affected by the duration of UV irradiation. Ultimate tensile strength and ultimate percentage elongation decreased after UV irradiation of the blend. Increasing UV irradiation leads to an increase in Young's modulus of the collagen/chitosan blend.     

Synthesis,reactions and catalytic activity of some mixed trifluorophosphine(triphenylphosphine)hydrido complexes of cobalt(I)

The complexes CoH(PF₃)_4?n (PPh₃)_n (n = 1–3) have been prepared by low from the reaction between CoH(PF₃)(PPh₃)₃ and butadiene. The hydrido complexes are active catalysts for the isomerisation of 1-octene to 2-octene under hydrogen or nitrogen.     

Synthesis of new mono-functionalised tetrathiafulvalene derivatives by reactions of etrathiafulvalenyllithium with aldehydes and ketones: X-ray crystal structures of TTF-CMe(OH)Fc, TTF-CMe(OMe)Fc and TTF-CH(OMe)TTF (Fc = ferrocenyl)

Reactions of tetrathiafulvalenyllithium (TTF-Li) with a range of aldehydes and ketones have been explored for the first time, to provide an efficient route to mono-functionalised TTF derivatives of general formulae TTF-CH(OH)R (R = alkyl, phenyl, tetrathiafulvalenyl and ferrocenyl) and TTF-CR(OH)R′ (R = alkyl, phenyl, R′ = alkyl, phenyl, tetrathiafulvalenyl, ferrocenyl, and R-R′ = fluorenyl). Subsequent transformations involving the reactive alcohol group of some of these compounds are reported. The structures of the three title compounds have been established by single-crystal X-ray analysis.     

Neutral pi-associated porphyrin [2]catenanes

A series of neutral porphyrin-containing catenanes has been synthesised, consisting of a zinc porphyrin strapped by a polyethylene glycol chain containing four or six ethylenoxy-units and incorporating a central naphthoquinol unit, interlinked with a naphthalene diimide macrocycle. The napthalene diimide precursor units exhibit only weak binding with the strapped porphyrins (Ka between 8 and 0.02 M(-1)), but good yields of the catenanes were obtained by Glaser coupling of the alkynyl napthalene diimide precursors in the presence of the porphyrins. Structures and solution conformations were determined by mass spectral and detailed 1H NMR studies. For the longer strapped porphyrins, the diimide macrocycle rotates around the central naphthoquinol unit at 420-450 times per second, while rotation is virtually prevented in the tighter strapped derivatives. A second dynamic process occurring in both sets of catenanes and described as 'yawing' leads to inequivalence in the naphthalene moieties. UV-Visible spectra indicate charge transfer interactions and electronic communication between the two components of the catenane.     

Synthesis and trapping of transient 1,2-diselones to yield 1,4-diselenin derivatives: calculated structures of 1,2-diselones, 1,2-diselenetes and their sulfur analogues

Two conceptually different routes to transient 1,2-diselones are reported: 1) via ring fragmentation of the 1,4,2-diselenazine system 6, and 2) by the tributylphosphane-induced depolymerisation of the shelf-stable organoselenium polymer 15. Evidence for the intermediacy of 1,2-diselone species 7 and 16 is provided in both cases by in situ trapping with dimethyl acetylenedicarboxylate (DMAD) to yield 1,4-diselenin derivatives. The route via 15 is especially expedient and trapping of 16 is efficient. Subsequent reactions of adduct 17 afford [1,2-ethanediylbis(diphenylphosphane)] [5,6-bis(methoxycarbonyl)-1,4-diselenin-2,3-dithiolato]nickel(IV) (20). Theoretical calculations at Hartree-Fock (HF) and Moller-Plesset electron-correlated levels (MP2) suggest that the cyclic 1,2-diselenete structure 7c is significantly more stable than the acyclic 1,2-diselone structure 7a. For the bicyclic system 16, the difference in energy between the cyclic and acyclic structures is considerably reduced due to the conformational rigidity imposed by the fused 1,3-dithiole ring. In contrast, the acyclic structures of the 1,2-dithione analogues 13a and 25a are computed to be more stable than their corresponding cyclic 1,2-dithiete structures 13c and 25c.     

Functionalized pyridylboronic acids and their Suzuki cross-coupling reactions to yield novel heteroarylpyridines

2-Bromo-5-pyridylboronic acid 2a, 2-chloro-5-pyridylboronic acid 2b, 2-methoxy-5-pyridylboronic acid 2c, and 5-chloro-2-methoxy-4-pyridylboronic acid 4 have been synthesized and shown to undergo palladium-catalyzed cross-coupling reactions with heteroaryl bromides to yield novel heteroarylpyridine derivatives. The X-ray crystal structures of 2a and 2b have been obtained.