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PubMed1991

Structures of 1-(3,3-dimethylamino)propyl naphtho[2,1-b]thiophene-4- carboxylate and N-(3,3-dimethylamino)propyl-8-methoxynaphtho[2,1- b]thiophene-4-carboxamide, intercalators into double-helical DNA.

(1) C18H19NO2S, Mr = 313.42, monoclinic, P2(1)/c, a = 11.503 (3), b = 15.932 (2), c = 9.133 (2) A, beta = 102.17 (2) degrees, V = 1636.1 A3, lambda(Cu K alpha) = 1.54178 A, mu = 1.762 mm-1, F(000) = 664, T = 293 (1) K, R = 0.047 for 2044 significant reflections. (2) C19H21NO3S, Mr = 343.45, triclinic, Pl, a = 9.873 (2), b = 13.163 (3), c = 14.065 (3) A, alpha = 101.33, beta = 94.30 (3), gamma = 91.35 (3) degrees, V = 1785.8 A3, Z = 4, Dx = 1.28 Mg m-3, lambda(Cu K alpha) = 1.54178 A, mu = 1.699 mm-1, F(000) = 728, T = 293 (1) K, R = 0.052 for 1787 significant reflections. The torsion angle between the naphthothiophene ring and the carbonyl O atom of the side chain is 5.5 (4) degrees in structure (1) and 25 (2) and -32 (2) degrees in the two independent molecules of (2). This difference is due to out-of-plane distortions in (2) that arise from steric hindrance between H atoms on the amide and the ring system, at position 2.

Intercalating Agents↗
PubMed2004

Adsorption, desorption, and conversion of thiophene on H-ZSM5.

The dynamics and stoichiometry of thiophene adsorption and of rearrangements of thiophene-derived adsorbed species in O(2), He, H(2), and C(3)H(8) carriers were measured using chromatographic methods and mass spectrometry on H-ZSM5 and H-Y zeolites. Thiophene adsorption obeyed Langmuir isotherms on both zeolites. Adsorption uptakes were 1.7 and 2.8 thiophene/Al at 363 K on H-ZSM5 and H-Y zeolites, respectively, after removal of physisorbed thiophene. These stoichiometries differed for these two zeolite structures but did not depend on their Al content (Si/Al = 13-85). Adsorption from a thiophene-toluene mixture showed thiophene selectivities ( approximately 10) greater than expected from van der Waals interactions. These adsorption stoichiometries, without contributions from physisorption, and the color changes detected indicate that thiophene adsorption occurs concurrently with oligomerization on acidic OH groups and that oligomer size depends on spatial constraints within channels. Thiophene oligomers decompose at approximately 534 K during subsequent thermal treatment to form molecular thiophene with all carriers, leaving behind unsaturated thiophene-derived species with a 0.9-1.1 thiophene/Al stoichiometry, confirming the specificity of OH groups and the oligomeric nature of bound thiophene during adsorption at 363 K. With He, H(2), and C(3)H(8), residual thiophene-derived species desorb as stable fragments, such as H(2)S, ethene, propene, arenes, and heavier organosulfur compounds (methylthiophene and benzothiophene) during thermal treatment; they also form unsaturated organic deposits that cannot desorb without hydrogenation events. H(2) and C(3)H(8) remove larger amounts of adsorbed species as unreacted thiophene than He, suggesting that dehydrogenation reactions are inhibited or reversed by a hydrogen source. C(3)H(8) removes a larger fraction of thiophene-derived intermediates as hydrocarbons and organosulfur compounds than H(2) or He; thus, hydrogen atoms formed during C(3)H(8) dehydrogenation are more effective in the removal of unsaturated deposits than those formed from H(2). Thiophene-derived adsorbed species are completely removed only with O(2)-containing streams at 873 K, a process that fully recovers initial adsorption capacities. This study provides a rigorous assessment of the nature and specificity of thiophene adsorption processes on acidic OH groups and of the identity and removal pathways of adsorbed species in various reactive environments.

Adsorption↗
PubMed1998

Chemolithoautotrophy and mixotrophy in the thiophene-2-carboxylic acid-utilizing xanthobacter tagetidis

Xanthobacter tagetidis grew as a chemolithotrophic autotroph on thiosulfate and other inorganic sulfur compounds, as a heterotroph on thiophene-2-carboxylic acid, acetic acid and alpha-ketoglutaric acid, and as a mixotroph on thiosulfate in combination with thiophene-2-carboxylic acid and/or acetic acid. Autotrophic growth on one-carbon organosulfur compounds, and intermediates in their oxidation are also reported. Thiosulfate enhanced the growth yields in mixotrophic cultures, presumably by acting as a supplementary energy source, since ribulose bisphosphate carboxylase was only active in thiosulfate-grown cells and was not detected in mixotrophic cultures using thiosulfate with thiophene-2-carboxylic acid. Bacteria grown on thiophene-2-carboxylic acid also oxidized sulfide, thiosulfate and tetrathionate, indicating these as possible sulfur intermediates in thiophene-2-carboxylic acid degradation. Thiosulfate and tetrathionate were oxidized completely to sulfate and, consequently, did not accumulate as products of thiophene-2-carboxylic acid oxidation in growing cultures. Km and Vmax values for the oxidation of thiosulfate, tetrathionate or sulfide were 13 &mgr;M and 83 nmol O2 min-1 (mg dry wt.)-1, respectively; thiosulfate and tetrathionate became autoinhibitory at concentrations above 100 &mgr;M. The true growth yield (Ymax) on thiophene-2-carboxylic acid was estimated from chemostat cultures (at dilution rates of 0.034-0.094 h-1) to be 112.2 g mol-1, with a maintenance coefficient (m) of 0.3 mmol thiophene-2-carboxylic acid (g dry wt.)-1 h-1, and the maximum specific growth rate (&mgr;max) was 0.116 h-1. Growth in chemostat culture at a dilution rate of 0. 041 h-1 indicated growth yields [g dry wt. (mol substrate)-1] of 8.1 g (mol thiosulfate)-1, 60.9 g (mol thiophene-2-carboxylic acid)-1, and 17.5 g (mol acetic acid)-1, with additive yields for growth on mixtures of these substrates. At a dilution rate of 0.034 h-1, yields of 57.8 g (mol alpha-ketoglutaric acid)-1 and 60.7 g (mol thiophene-2-carboxylic acid)-1 indicated some additional energy conservation from oxidation of the thiophene-sulfur. SDS-PAGE of cell-free preparations indicated a polypeptide (Mr, 21.0 kDa) specific to growth on thiophene-2-carboxylic acid for which no function can yet be ascribed: no metabolism of thiophene-2-carboxylic acid by cell-free extracts was detected. It was shown that X. tagetidis exhibits a remarkable degree of metabolic versatility and is representative of facultatively methylotrophic and chemolithotrophic autotrophs that contribute significantly to the turnover of simple inorganic and organic sulfur compounds (including substituted thiophenes) in the natural environment.

Journal Article↗
PubMed2002

Mechanism of the aromatic hydroxylation of thiophene by acid-catalyzed peracid oxidation.

The oxidation of thiophene (1) with peracids in a strongly acidic environment yielded thiophen-2-one (4) as the product of an apparent direct hydroxylation of the thiophene aromatic ring together with the anticipated thiophene-S-oxide dimers, 2a,b, as the main products. Formation of the latter dimers can be rationalized in a straightforward manner by initial oxidation at the sulfur atom of thiophene (1) to yield thiophene-S-oxide followed by subsequent dimerization in a Diels-Alder type reaction. Trapping experiments in the presence of a competing dienophile indicated that thiophen-2-one (4) did not originate from the monomeric thiophene-S-oxide but was the product of an independent reaction pathway. The extent of thiophen-2-one (4) formation correlated with the acidity of the reaction medium and was suppressed in the presence of water, the latter presumably acting as a competing base. As evidenced by the use of 2,5-dideuterated thiophene (1-D), its mechanism of formation involved a 1,2-hydride shift, a feature commonly described in the peracid-mediated epoxidation of aromatic hydrocarbons and indicative for the occurrence of cationic intermediates. In agreement with all these observations we propose a mechanism involving initial protonation of thiophene followed by nucleophilic attack of the peracid in position 2 of the thiophene ring. Intramolecular epoxidation may lead to the formation of thiophene 2,3-epoxide as a highly reactive intermediate that then undergoes heterolytic ring opening and a 1,2-hydride shift to yield thiophen-2-one (4) after a final, acid-catalyzed, isomerization of the double bond.

Journal Article↗
PubMed1993

Pulmonary absorption and disposition of [14C]thiophene in rats following nose-only inhalation exposure.

The absorption, disposition, and metabolism of [14C]thiophene was investigated in rats following nose-only inhalation exposure at 8000 ppm for 1 h. Under these exposure conditions, it was estimated that approximately 16.3% (493 mumol) of the inhaled thiophene was absorbed from the respiratory system. Within 72 h following exposure, a total of 488 mumol of thiophene equivalents (99% of that retained) was excreted, of which 360.4 mumol (73.9% of the total excreted radioactivity) was in expired air, 120.7 mumol (24.8%) was in urine, 3 mumol (0.6%) was in feces, and 3.7 mumol (0.8%) was in the cage wash. Excretion took place primarily within the first 8 h, during which 91% of the total radioactivity excreted was collected. The thiophene equivalents remaining in tissues at 72 h were estimated to total 5.1 mumol (1.0% of the retained radioactivity). Exhaled radioactivity was identified as thiophene. No 14CO2 was detected in the expired air. After 1 h following exposure, the elimination of thiophene equivalents from plasma was monophasic, with a half-time of 3.6 h. The elimination of thiophene equivalents from blood cells was biphasic, with half-times of 2.9 h and 9.1 d. The blood cells/plasma concentration ratios of thiophene equivalents ranged from 3 to 13, with the higher ratio observed at the 12-h time interval. At 72 h after exposure, blood cells contained the highest concentration of thiophene equivalents, approximately fourfold higher than that of the liver, which contained the second highest concentration. Kidney, heart, and lung contained similar but lower concentrations than liver, while brain, fat, and skeletal muscles contained the lowest concentrations. In summary, this study demonstrates that thiophene was absorbed from the respiratory system, and the majority of the absorbed thiophene was eliminated unchanged in the exhaled air, while a smaller fraction was metabolized and eliminated in urine.

Absorption↗