Triplet-triplet absorption spectra of quinoline and isoquinoline

The difference between the singlet-singlet and the triplet-triplet absorption spectra of quinoline and isoquinoline has been measured from 45 000 to 15 000 cm^?1, in a rigid hydrocarbon glass at 77 K, using a newly constructed computer controlled spectrograph. Both molecules show strong new triplet-triplet absorption bands in the ultraviolet region. Similar bands have recently been found in naphthalene and were assigned to transitions from the lowest triplet state to a triplet state which is doubly excited with respect to the closed shell ground state.     

The quenched Eguchi-Kawai model

It is argued that spontaneous symmetry breaking occurs in the recently proposed Eguchi-Kawai model. The argument is based on an analytic investigation and on Monte Carlo simulations. A quenched version of the model is proposed which gives good behavior at weak couplings.     

Laser excited luminescence of coronene in a shpolskii matrix

The luminescence spectrum of coronene in n-heptane at 77°K has been studied using both xenon lamp and argon ion laser excitation. The results illustrate the Shpolskii theory of different emitting sites. With xenon excitation the emission spectrum consists of two similar slightly shifted subspectra. With laser excitation at 3511 Å only the longer wavelength subspectrum is observed. Fluorescence and phosphorescence excitation spectra show that this laser line is absorbed by the longwave component of the S₂←S₀ doublet.     

Metric stability of trees and tight spans

We prove optimal extension results for roughly isometric relations between metric ( ${\mathbb{R}}$ R -)trees and injective metric spaces. This yields sharp stability estimates, in terms of the Gromov–Hausdorff (GH) distance, for certain metric spanning constructions: the GH distance of two metric trees spanned by some subsets is smaller than or equal to the GH distance of these sets. The GH distance of the injective hulls, or tight spans, of two metric spaces is at most twice the GH distance between themselves.     

Strychnine-8-ammonio-2-naphthalenesulfonate-water (1/1/3.5): The first structure of a strychnine or brucine compound with a zwitterionic species

The crystal structure of the 1:1 adduct hydrate of strychnine with 1,7-Cleve's acid (8-amino-2-naphthalenesulfonic acid), namely strychnine-8-ammonio-2-naphthalenesulfonate-water (1/1/3.5) has been determined and provides a unique example of a neutral association involving strychnine and an achiral zwitterionic acid species, previously unobserved in the structures of either strychnine or brucine addition compounds. Crystals are orthorhombic, space group P2₁2₁2₁, with Z=4 in a cell with dimensions a=10.4484(8), b=30.850(3), c=9.4998(11) ?. Hydrogen bonding involving all available proton-donor and acceptor sites on all species gives rise to a three-dimensional framework polymer structure. The crystallographic literature for strychnine and brucine and their compounds is also reviewed.     

Two‐ and three‐dimensional hydrogen‐bonded structures in the 1:1 proton‐transfer compounds of 4,5‐dichlorophthalic acid with the isomeric monoaminobenzoic acids

The crystal structures of the 1:1 proton‐transfer compounds of 4,5‐dichlorophthalic acid with the three isomeric monoaminobenzoic acids, namely the hydrate 2‐carboxyanilinium 2‐carboxy‐4,5‐dichlorobenzoate dihydrate, C₇H₈NO₂⁺·C₈H₃Cl₂O₄⁻·2H₂O, (I), and the anhydrous salts 3‐carboxyanilinium 2‐carboxy‐4,5‐dichlorobenzoate, C₇H₈NO₂⁺·C₈H₃Cl₂O₄⁻, (II), and 4‐carboxyanilinium 2‐carboxy‐4,5‐dichlorobenzoate, C₇H₈NO₂⁺·C₈H₃Cl₂O₄⁻, (III), have been determined at 130 K. Compound (I) has a two‐dimensional hydrogen‐bonded sheet structure, while (II) and (III) are three‐dimensional. All three compounds feature sheet substructures formed through anilinium N⁺—H...O_carboxyl and anion carboxylic acid O—H...O_carboxyl interactions and, in the case of (I), additionally linked through the donor and acceptor associations of the solvent water molecules. However, (II) and (III) have additional lateral extensions of these substructures though cyclic R²₂(8) associations involving the carboxylic acid groups of the cations. Also, (II) and (III) have cation–anion π–π aromatic ring interactions. This work provides further examples illustrating the regular formation of network substructures in the 1:1 proton‐transfer salts of 4,5‐dichlorophthalic acid with the bifunctional aromatic amines.     

The three‐dimensional hydrogen‐bonded framework structure in the 1:1 proton‐transfer compound of the drug quinacrine with 5‐sulfosalicylic acid

For the hydrated proton‐transfer compound 6‐chloro‐9‐[(4‐diethylammonio‐2‐methylbutyl)amino]‐2‐methoxyacridinium 3‐carboxylato‐4‐hydroxybenzenesulfonate dihydrate, C₂₃H₃₂ClN₃O²⁺·C₇H₄O₆S²⁻·2H₂O, (I), the conformational features, specifically those of the extended side chain at the 9‐position of the acridine parent, have been compared with those of quinacrinium dichloride dihydrate (the drug atabrine or mepacrine). Racemic compound (I) has a three‐dimensional hydrogen‐bonded framework structure similar to atabrine but also involves the water molecules and both the carboxylate and sulfonate groups of the anion in structure extension. The comparable conformational features found in this uncommon derivative of quinacrine indicate that (I) has potential as a possible pharmaceutical substitute for atabrine.     

Identification of polyoxypregnane glycosides from the stems of Marsdenia tenacissima by high-performance liquid chromatography/tandem mass spectrometry

A facile method based on high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC/(+)ESI-MSⁿ) has been established for the analysis of polyoxypregnane glycosides in the stems of Marsdenia tenacissima. The data reveals the ability of MSⁿ in the structural elucidation of polyoxypregnane glycosides including the nature of the polyoxypregnane core, the kinds of the substituents and the types of sugar residues. Offline Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is also performed to assign accurate elemental compositions. In this study, eighteen polyoxypregnane glycosides have been investigated. Among these components, five compounds are unambiguously identified as Marsdenoside K, Tencissoside A, B, C and D; two compounds are established as novel compounds based on mass spectral data; and the other eleven compound's structures are tentatively proposed. Furthermore, breakdown curves are constructed to distinguish five pairs of isomers among these eighteen compounds. As far as our knowledge, this is the first report on identification of polyoxypregnane glycosides in the stems of M. tenacissima by HPLC/ESI-MSⁿ directly, which could save time and material consuming efforts in traditional phytochemistry analyses.