The Dyeing of Nylon and Cotton Cloth with Azo Dyes: Kinetics and Mechanism

The mechanism of the dyeing of cotton and nylon cloth by the azo dyes Orange G and Sunset Yellow FCF was investigated using a channel flow cell. The variation in dyeing with flow rate was found to proceed via a mechanism in which the flux of dye entering the cloth relative to the flux of dye to the cloth surfacedecreasedwith increasing flow rate. A mechanism is deduced in which the dye passes from bulk solution, through a porous surface layer within the cloth, before passing into the bulk cloth. Adsorption onto surface sites in this porous layer blocks the passage of further dye into the cloth. Kinetic parameters for such a mechanism are given.     

Long-range fluorine-proton coupling in 1,2,4-triazole derivatives

Several 1,2,4-triazole derivatives containing a 2-fluorophenyl substituent at either the 3- or 5-position and a methyl group at the 4-position were synthesized. These derivatives exhibit long-range ¹⁹F-¹H and ¹⁹F-¹³C through-space coupling in their ¹H and ¹³C nmr spectra between the fluorine and the 4-methyl group. The close spatial proximity of these nuclei was confirmed by X-ray analysis and by fluorine irradiated proton observe ({¹⁹F}-¹H) NOE difference spectroscopy.     

Synthesis and structure of The Novel Layered Phase CsTi2Cl7

Reactions in the CsCl? TiCl₃? Ti system afford CsTiCl₃ (CsNiCl₃ type, a = 7.3086(7) Å, c = 6.0670(8) Å) and the new phase CsTi₂Cl₇, the structure of which was determined by single crystal X-ray diffraction means (P2/c, Z = 2, a = 7.0076(4) Å, b = 6.2256(4) Å, c = 12.000(2) Å, β = 92.175(6)°, R/R_w = 0.026/0.035 for 1403 reflections, 2Θ ≤ 60°, MoKα). The structure can be generated by condensation of TiCl₆ groups first through cis edges to form TiCl₂Cl_4/2 ribbons and then by interconnection of these with one chlorine per titanium to give layers, viz., [Ti(Cl)Cl_4/2Cl_1/2]^?. The remaining, singly bonded chlorine projects into the interlayer region and has a Ti? Cl distance 0.208 Å less than the average for the five, 2.466 Å, reflecting significant pi bonding of the chlorine to titanium. Possible interaction of the d orbitals on adjacent titanium(III) atoms is also considered.     

Electron transfer reactions of cytochrome c at metal electrodes

The heterogeneous electron transfer reactions of cytochromec occurring at platinum, gold and mercury electrodes are shown to be quasi-reversible. In each case the electrodes have not been modified and the cytochromec samples are native. This work extends previous work and demonstrates that biological molecule electron transfer reactions can be studied at clean metal surfaces to gain fundamental knowledge of the mechanisms of these reactions.     

Observation and interpretation of HH coupling in 1H187Os satellite NMR spectra

The single hydride resonance observed for each of the compounds H₃Os₃(CO)₉CX (X = OMe, Br, H) has one set of ¹⁸⁷Os satellites which are further split into doublets by HH coupling. The implications of this observation for structural assignments based on ¹⁸⁷Os satellites are discussed.     

Recent developments in the maytansinoid antitumor agents

Maytansine and its congeners have been isolated from higher plants, mosses and from an Actinomycete, Actinosynnema pretiosum. Many of these compounds are antitumor agents of extraordinary potency, yet phase II clinical trials with maytansine proved disappointing. The chemistry and biology of maytansinoids has been reviewed repeatedly in the late 1970s and early 1980s; the present review covers new developments in this field during the last two decades. These include the use of maytansinoids as "warheads" in tumor-specific antibodies, preliminary metabolism studies, investigations of their biosynthesis at the biochemical and genetic level, and ecological issues related to the occurrence of such typical microbial metabolites in higher plants.     

Vitamin B12 as an allosteric cofactor; dual fluorescence, hysteresis, oscillations and the selection of corrin over porphyrin

Studies of the emission spectra of four Co(III) cobinamides (diaquo-, aquohydroxo-, dihydroxo- and dicyano-) show (1) that the excited states corresponding to the alphabeta and epsilon absorption bands behave like the S(1) and S(2) levels in the non-alternant hydrocarbon azulene (with emission from S(2)> S(1) in violation of Kasha's rule) and (2) that the excited states include a TICT (twisted intramolecular charge transfer) mechanism, as in the simpler cyanines, but where the TICT state gives rise to dual fluorescence instead of cis-trans isomerisation. Combined with the previously reported dual fluorescence from the S(1) level in synthetic metal corrinoids and in the naturally-occurring metal-free corrin, this provides evidence that the existence of an additional (metastable) ground state with a significantly different vibronic splitting and nuclear configuration is an intrinsic property of the basic corrin ligand (irrespective of the nature of the side-chains and the metal ion or even the absence of a metal) which distinguishes it from porphyrin. The occurrence of hysteresis (and its associated oscillations) in redox reactions of the cobinamides involving both the Co(III/II) and Co(II/I) couples indicates that the corrin ligand also has an intrinsic ability to exist in different conformations or "allosteric" forms with differing redox potential, which further distinguishes it from the porphyrin ligand. Possible links between the existence of an additional metastable ground state and of allosteric changes and the likely reasons for the selection of corrin over a porphyrin for the vitamin B(12)-dependent enzymes are discussed.     

Ring expansion-annulation strategy for the synthesis of substituted azulenes and oligoazulenes. 2. Synthesis of azulenyl halides, sulfonates, and azulenylmetal compounds and their application in transition-metal-mediated coupling reactions

A "ring expansion-annulation strategy" for the synthesis of substituted azulenes is described based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates. The key transformation involves an intramolecular Buchner reaction followed by beta-elimination of bromide, tautomerization, and in situ trapping of the resulting 1-hydroxyazulene as a carboxylate or triflate ester. Further synthetic elaboration of the azulenyl halide and sulfonate annulation products can be achieved by employing Heck, Negishi, Stille, and Suzuki coupling reactions. Reaction of the azulenyl triflate 84 with pinacolborane provides access to the azulenylboronate 91, which participates in Suzuki coupling reactions with alkenyl and aryl iodides. The application of these coupling reactions to the synthesis of biazulenes, terazulene 101, and related oligoazulenes is described, as well as the preparation of the azulenyl amino acid derivative 110.     

Aporphines 24. The synthesis of N-alkylderivatives of bulbocapnine and isoeorydine

The synthesis of three new racemic aporphine alkaloids ( 1b, 1c and 2 ) is reported and these alkaloids are fully characterized. The method of synthesis involved either a Bischler-Napieralski-Psehorr sequence or a Reissert alkylation-Pschorr cyclization route. The Pschorr cyclization also gave the morphinandienones 7a and 7b , respectively.     

A novel,stereoselective silyl-directed Stevens [1,2]-shift of ammonium ylides

[reaction: see text] The silyl group of 2-silylpyrrolidines such as 1 plays several critical roles: a stereochemical control element in a facially selective carbenoid addition to the ring nitrogen, a stereochemical "placeholder" during regioselective 1,2-migration with retention by the resulting spirocyclic ammonium ylide, and a hydroxyl surrogate for an eventual stereoselective Fleming-Tamao oxidation. This chemistry represents a novel use of the Stevens rearrangement and offers a short, enantioselective route to hydroxylated quinolizidines such as 3 from Boc-pyrrolidine.