Dipyrrolyldiketone difluoroboron complexes: novel anion sensors with C-H...X- interactions

1,3-Dipyrrolyl-1,3-propanediones, synthesized from pyrroles and malonyl chloride, form BF2 complexes, which represent a new class of naked-eye sensors for halide and oxoanions. The association mode for the interactions of both the pyrrolyl NH and bridging CH protons with anions was confirmed by 1H NMR chemical shifts in CD2Cl2 and supported by theoretical studies. The binding constants (Ka) were estimated as 8.1x10(4), 2.0x10(3), 3.3x10(2), 1.3x10(4), and 80 M(-1) for F-, Cl-, Br-, H2PO4(-), and HSO4(-) by UV/Vis absorption spectral changes in CH2Cl2. Augmentation of Ka compared with dipyrrolylquinoxaline for H2PO4(-) is much larger than those for other anions. Contrary to other anions, F- quenches the emission almost completely, which was detected by the fluorescence spectrum as well as the naked-eye. In the case of the chloride anion complex, the formation of Cl(-)-bridged 1D networks, in which anion is associated with two BF2 complexes, is observed in the solid state.     

Indole alkaloids from Kopsia jasminiflora

Seven new indole alkaloids (aspidofractinine type 1–3, kopsine type 5, strychnos type 6, and vincamine type 7, 8) were isolated from Kopsia jasminiflora (Apocynaceae) collected in Thailand. 5-Oxokopsinic acid (4) was isolated from nature for the first time. The structures of the new alkaloids were determined by spectroscopic analyses and chemical transformation of a known alkaloid. 5,6-Secokopsinine (1) possesses a dialdehyde function that is formed by oxidative cleavage of the C-5–C-6 bond of kopsinine (9). New vincamine-type alkaloid 8 showed potent inhibitory activity toward human cancer cell lines (A549, HT29, HCT116).     

Constituents of regenerated plants of Ophiorrhiza pumila; formation of a new glycocamptothecin and predominant formation of (3R)-deoxypumiloside over (3S)-congener

The regeneration of plantlets was successful from Ophiorrhiza pumila callus cultures, from which a new glucosyloxy camptothecin, 9-β-glucosyloxycamptothecin, together with 15 metabolites including six camptothecin-related alkaloids was isolated. (3S)-Deoxypumiloside, one of the plausible biogenetic precursors of camptothecin, could not be found, whereas the (3R) epimer was isolated from the regenerated plants.     

Flow characteristics and spinnability of sols prepared from silicon alkoxide solution

Structural evolution of the solution of tetraethoxysilane hydrolyzed with [H₂O]/[Si(OC₂H₅)₄] = 2 under acidic condition has been investigated by rheological measurements. It was found that the solution behaves as a Newtonian liquid up to a highly viscous state and shows spinnability before gelation when the evaporation of the solvent is allowed during gelation reaction. On the other hand, the solution behaved as a non-Newtonian liquid in the viscous state, showing no spinnability when the evaporation of the solvent was not allowed during the reaction. It was indicated from the Casson plots that the spinnable solution prepared in the open system has no yield stress up to highly viscous states, whereas the non-spinnable solution prepared in the closed system has a yield stress at viscous states. It was proposed that the increase in viscosity of the open system solution is attributable to the concentration of the sol particles whereas that of the closed system solution is attributable to the formation of the three dimensional network in the solution.     

Synthesis of soluble quinacridones

The synthesis of 4,11-dialkylthioquinacridones and 5,12-dialkyl-4,11-dialkylthioquinacridone from o-alkylthioanilines and diethyl 2,5-dioxo-1,4-cyclohexanedicarboxylate is described. These compounds are easily soluble in organic solvents in contrast to unsubstituted quinacridone.     

High temperature pyrolysis of formaldehyde in shock waves

Thermal decomposition of formaldehyde diluted with Ar was studied behind reflected shock waves in the temperature range of 1200–2000 K at total pressures between 1.3 and 3.0 atm. The study was carried out for compositions from the concentrated mixture, 4% CH₂O, to the highly dilute mixture, 0.01% CH₂O by using time-resolve IR-laser absorption and IR-emission, and a single-pulse technique. From a computer-simulation study, the mechanism and the rate-constant expressions that could explain all of our data and previously reported ARAS data were discussed. This data obtained over a wide concentration range from 50 ppm CH₂O to 4% CH₂O were satisfactorily modeled by a five-reaction mechanism. © 1993 John Wiley & Sons, Inc.     

Rearrangement of tertiary amine N-oxides—XXVII Mechanism of the reaction of isoquinoline N-oxide with substituted benzenesulfonyl chlorides

Kinetic experiments have been carried out on the reactions of isoquinoline N-oxide with p-toluenesulfonyl and other substituted benzenesulfonyl chlorides, varying solvent and salt compositions. The rate was correlated by the second-order equation, i.e., v = [N → O] × [ArSO₂Cl], and was found to be accelerated in polar media. The addition of chloride ion was found to increase the rate considerably, while the rates of the over-all reaction became greater with arenesulfonyl chlorides bearing stronger electron-withdrawing substituents ( = +2·0). By the use of 1-deuterated isoquinoline N-oxide a small kinetic isotope effect (k_H/k_D = 1·2) was observed for this reaction. Based on these kinetic observations the rate-determining step of this reaction is considered to be the cleavage of N---O bond. Meanwhile, from the ¹⁸O-tracer experiments in several solvents using uniformly ¹⁸O-labelled p-toluenesulfonyl or p-bromobenzenesulfonyl chloride the migration of arenesulfonate was found to proceed mainly via oxygen-bridged ion pair pathway.     

Trans doubly N-confused porphyrins: Cu(III) complexation and formation of rodlike hydrogen-bonding networks

A trans type of doubly N-confused isomer of NCP (trans-N2CP) was synthesized via N-confused fused porphyrin (NcFP). The aromatic feature of trans-N2CP due to 18pi electronic system is contrasted to the weak aromaticity of cis-derivative. The solid-state structure of trans-N2CP exhibits pi-stacking column, while the Cu(III) complex shows 1-D rodlike hydrogen bonding chain comparable with the zigzag hydrogen-bonding chain of cis-derivatives.     

Murexide reaction of caffeine with hydrogen peroxide and hydrochloric acid. II

In continuation of the study on the murexide reaction of caffeine with 3% hydrogen peroxide/hydrochloric acid and then with ammonia giving a purple coloration, we investigated the oxidation reaction of caffeine with 6% hydrogen peroxide/hydrochloric acid to isolate ten reaction products, 3-hydroxy-4,6-dimethyloxazolo[4,5-d]pyrimidine-2,5,7(3H,4H,6H)-trione 1 , 1,3-dimethylalloxan 2 , murexoin 3 , 1,3,7-trimethyl-2,6,8-trioxo-9-hydroxy-1H,3H,7H-xanthine 5 , 1,3,7-trimethyl-2,6,8-trioxo-1H,3H,7H-xanthine 6 , 1,3,7-trimethyl-2,6-dioxo-8-chloro-1H,3H,7H-xanthine 7, 5-(1,3-dimethyl-1,2,3,4,5,6-hexahydro-2,4,6-trioxopyrimidin-5-yl)-aminomethylene-1,3-dimethyl-1,2,3,4,5,6-hexahydro-2,4,6-trioxopyrimidine ammonium salt 9 , 1,3-dimethylpalabanic acid 10 , 1-methyl-2,4,5-trioxoimidazole 11 , 3-hydroxy-5,7-dimethyloxazolo[5,4-d]pyrimidine-2,4,6(3H,5H,7H)-trione 12 and 4,6,8-trimethyl-1,2,4-dioxazino[6,5-d]pyrimidine-3,5,7(4H,6H,8H)-trione 13 . The oxidation reaction using 6% hydrogen peroxide/hydrochloric acid was found to produce a similar purple coloration to that of the murexide reaction despite no subsequent addition of ammonia, indicating the liberation of ammonia by the oxidation of caffeine. Among the above compounds, the purple colored substance murexoin 3 and the yellow colored compound 9 were both ammonium salts, and compound 5 was the red colored substance. In the present investigation, these three compounds were found to contribute to the coloration.     

Micro‐ and Nanometer‐Scale Porous,Fibrous, and Sheet Architectures Constructed by Supramolecular Assemblies of Dipyrrolyldiketones

X‐ray analysis of some 1,3‐dipyrrolyl‐1,3‐propanediones synthesized from pyrroles and malonyl chloride derivatives revealed 1D supramolecular networks formed by N? H???O?C interactions in the solid state. Micro‐ and nanometer‐scale morphologies of porous, fibrous, and sheet structures were fabricated by hydrogen‐bonding interactions and determined by fine‐tuning the substituents and the solvents used. Of the unique polymorphs, ordered 2D lamellar sheet structures of the derivatives with long alkyl chains (C₁₆H₃₃, C₁₄H₂₉, and so on) were constructed by van der Waals hydrophobic effects between aliphatic chains as well as hydrogen bonding.