What is the form of muscimol from fly agaric mushroom (Amanita muscaria) in water? An insight from NMR experiment supported by molecular modeling

The biologically active alkaloid muscimol is present in fly agaric mushroom (Amanita muscaria), and its structure and action is related to human neurotransmitter _γ-aminobutyric acid (GABA). The current study reports on determination of muscimol form present in water solution using multinuclear ¹H and ¹³C nuclear magnetic resonance (NMR) experiments supported by density functional theory molecular modeling. The structures of three forms of free muscimol molecule both in the gas phase and in the presence of water solvent, modeled by polarized continuous model, and nuclear magnetic isotropic shieldings, the corresponding chemical shifts, and indirect spin–spin coupling constants were calculated. Several J-couplings observed in proton and carbon NMR spectra, not available before, are reported. The obtained experimental spectra, supported by theoretical calculations, favor the zwitterion form of muscimol in water. This structure differs from NH isomer, previously determined in dimethyl sulfoxide (DMSO) solution. In addition, positions of signals C3 and C5 are reversed in both solvents.     

Level structure of 68 149 Er81 and high-spin isomerism in proton-richN=81, 82, 83 nuclei

The level structure of theN=81 nucleus¹⁴⁹Er has been studied by γ-ray spectroscopy following the reaction⁹²Mo+255 MeV⁶⁰Ni. Yrast levels in¹⁴⁹Er are established up to ~3.3 MeV, including 0.61 and 4.8 μs isomeric states. Most of the observed levels are interpreted as seniority-three states arising from the coupling of s_1/2, d_3/2 and h_11/2 neutron holes with πh ₁₁ ^2/n . Isomers identified in the reaction⁹⁶Ru+255 MeV⁵⁸Ni are tentatively assigned to¹⁵¹Yb. TheB (E2) values of high-spin isomers inZ=66?70,N=81?83 nuclei are surveyed.     

Hemmung der aktiven Bromidaufnahme durch Pflanzenzellen durch Glucose

Zusammenfassung Die Aufnahme von Bromid-Ion durch Chlorella pyrenoidosa, die durch aktiven Transport erfolgt, wird durch Glucose gehemmt, obwohl die Atmung stimuliert wird. Die Hemmung tritt bei Energielieferung durch Belüftung oder Belichtung ein. Galactose und Mannit wirken nicht wie Glucose. Offenbar hemmt die Glucose die Nutzbarmachung des Elektronenflusses bei dem System der Atmung oder Photophosphorylierung für die Bromid-Aufnahme.

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The absorption of bromide ion by chlorella pyrenoidosa, which is due to active transport, is inhibited by glucose though respiration is stimulated. Inhibition is observed when energy is supplied either by aeration or by illumination. Galactose or mannitol do not act like glucose. Apparently glucose interferes with the utilization of electron flow in the respiration or photophosphorylation systems for the absorption of bromide.

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Mit 3 Abbildungen.

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Herrn Prof. Dr.F. Wessely zum 70. Geburtstag in Verehrung gewidmet.     

Preferred dimerization of tetra-tolyl- and tetra-tosylurea derivatives of flexible and rigidified calix[4]arenes

The dimerization of tetratolyl- and tetratosyl-urea derivatives 1 and 2, derived from a tetrapentoxy calix[4]arene in the cone conformation and of the corresponding tetra-urea derivatives 3 and 4, in which the cone conformation is rigidified by the two crown-3 tethers, have been studied. All six possible equimolar mixtures were examined by 1H NMR using CDCl3 and CD2Cl2 as solvents. While no heterodimers are found for the combinations 1/3 and 2/4 in either solvent, all remaining combinations lead to the (exclusive) formation of heterodimers in CD2Cl2. In CDCl3 heterodimers are only observed for the combinations of 3 with 2 or 4. These results are discussed in terms of entropic and enthalpic contributions and compared with MD-simulations in a box of chloroform solvent molecules.     

Orthorhombic polymorphs of two trans‐4‐aminoazoxybenzenes

The two isomeric compounds 4‐amino‐ONN‐azoxy­benzene [or 1‐(4‐amino­phenyl)‐2‐phenyl­diazene 2‐oxide], i.e. the α isomer, and 4‐amino‐NNO‐azoxy­benzene [or 2‐(4‐amino­phenyl)‐1‐phenyl­diazene 2‐oxide], i.e. the β isomer, both C₁₂H₁₁N₃O, crystallized from a polar solvent in orthorhombic space groups, and their crystal and molecular structures have been determined using X‐ray diffraction. There are no significant differences in the bond lengths and valence angles in the two isomers, in comparison with their monoclinic polymorphs. However, the conformations of the mol­ecules are different due to rotation along the Ar—N bonds. In the α isomer, the benzene rings are twisted by 31.5 (2) and 14.4 (2)° towards the plane of the azoxy group; the torsion angles along the Ar—N bond in the β isomer are 24.3 (3) and 23.5 (3)°. Quantum‐mechanical calculations indicate that planar conformations are energetically favourable for both isomers. The N—H?O hydrogen bonds observed in both networks may be responsible for the deformation of these flexible mol­ecules.     

Die empfindliche Serienbestimmung von Radiokohlenstoff mit einem Gaszählrohr

Zusammenfassung Die Leistungsfähigkeit verschiedener Methoden zur empfindlichen Serienmessung von Radiokohlenstoff wird verglichen. Eine Methode wird beschrieben, bei der der Kohlenstoff in Form von ungereinigtem, zusatzfreiem Kohlendioxyd zum Füllen eines Zählrohres verwendet wird. Der Fülldruck kann 1 Atmosphäre und mehr betragen. Fast steigungsfreie Konstanzbereiche von einer Länge bis zu 1200 V werden erhalten. Ein Gehalt des Gases an Wasserdampf schadet nicht, ein Gehalt an Luft erst bei einem Partialdruck von mehreren Millimetern Quecksilber.

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Summary A comparison was made of the efficiency of various methods for the sensitive serial measurements of radio carbon. A method is described in which the carbon used for filling a counting tube was in the form of nonpurified, additive-free carbon dioxide. The filling pressure may be 1 atmosphere and more. Plateaus practically free from increases were obtained from a length up to 1200 volts. No harm results if the gas contains water vapor, and air does not interfere until its partial pressure exceeds several millimeters of mercury.

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Résumé On compare la valeur de plusieurs méthodes en vue de la mesure en série du radiocarbone de façon sensible. On décrit une méthode suivant laquelle on remplit le tube-compteur avec du gaz carbonique non purifié et exempt de toute addition. La pression du remplissage peut s'élever jusqu'à 1 atmosphère et plus. On obtient des valeurs constantes qui n'augmentent pour ainsi dire pas, jusqu'à 1200 volts. La présence de vapeur d'eau dans le gaz ne gêne pas, celle de l'air non plus, jusqu'à une pression partielle de plusieurs millimètres de mercure.

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Herrn Prof. Dr.-Ing.F. Feigl in Verehrung zum 70. Geburtstag gewidmet.

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In Dankbarkeit gedenktE. B. des unermüdlichen Interesses, das der damalige DozentFeigl den Anfängern in seinem Saale entgegenbrachte, und des Enthusiasmus, den er auf sie übertrug.     

Impact of the ΔPhe configuration on the Boc-Gly-ΔPhe-NHMe conformation: experiment and theory

Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is significantly lower for the E isomer (Boc-Gly-(E)-ΔPhe-NHMe), both in gas phase and in chloroform solution.