Electrospray ionization mass spectrometric detection of self-assembly of a crown ether complex directed by π-stacking interactions

The self-assembly of ligand-metal-ligand sandwich complexes involving a novel quinoxaline-containing crown ether, 1, was studied by electrospray ionization mass spectrometry (ESI-MS). Donor-acceptor π-stacking interactions between the electron-poor quinoxaline group of 1 and electron-rich benzene groups from benzo- or dibenzo-18-crown-6 were found to significantly enhance the formation of mixed-ligand sandwich complexes with a free energy gain of up to 17 kJ/mol relative to sandwich formation involving macrocycles without such aromatic functionalities. The relative intensities of the sandwich complexes were greatest with the alkali metals Na⁺, K⁺, and Rb⁺ as well as with the ammonium ion in equimolar concentrations with the macrocycles. The preferential formation of the mixed-ligand sandwich complexes demonstrated that donor-acceptor π-stacking interactions contribute to the assembly of molecular structures and can be monitored by ESI-MS.     

Polarization of 22 MeV neutrons elastically scattered from liquid tritium

The asymmetries from elastic scattering of 22.1 MeV incident neutrons was measured for 11 laboratory angles between 40° and 118.5°. The extrema are −60% at 85° (lab) and +98% at 110° (lab).     

Completely normal matrices

Normal matrices in which all submatrices are normal are said to be completely normal. We characterize this class of matrices, determine the possible inertias of a particular completely normal matrix, and show that real matrices in this class are closed under (general) Schur complementation. We provide explicit formulas for the Moore–Penrose inverse of a completely normal matrix of size at least four. A result on irreducible principally normal matrices is derived as well.     

Weakly first-order or nearly second-order phase transitions in ammonium halides

This work is mainly concerned with the application to the ammonium chloride system of the model that was developed by Yurtseven (1993).

Using the model, which is an Ising model superimposed on an Einstein and/or Debye model, the specific heat C _v has been calculated in the vicinity of the λ-phase transition in NH₄Cl.

Our calculated C _v values give a reasonable fit to the observed more recent C _p data from the literature.

The model predictions applicable to the ammonium halides are discussed.     

Isolation of a new indoxyl alkaloid,Amoenamide B,from Aspergillus amoenus NRRL 35600: Biosynthetic implications and correction of the structure of Speramide B

A new prenylated indoxyl alkaloid, Amoenamide B (1), was isolated from Aspergillus amoenus NRRL 35600 along with Asperochramide A (2). Although many prenylated oxindole alkaloids, containing bicyclo[2.2.2]diazaoctane cores, have been isolated from the fungus of the genera Aspergillus and Penicillium to date, 1 is the fourth compound with the indoxyl unit containing the cores. During the structure elucidation of 1, we found that the planar structure matched to that of Speramide A (3), isolated from A. ochraceus KM007, but the reported structure of 3 was incorrect and turned out to be that of Taichunamide H (4), recently isolated from A. versicolor HDN11-84.