Ikirydinium A: a new indole alkaloid from the seeds of Hunteria umbellata (K. Schum)

Chemical investigations into samples of Hunteria umbellata (K. Schum) collected in Osun State, Nigeria, led to the discovery of a new indole alkaloid, ikirydinium A, featuring an unprecedented 3-alkylpyridinium-indole-2-carboxylate scaffold. Ikirydinium A was found to exhibit antimicrobial activity (IC₅₀ 0.6 μM) against Bacillus subtilis ATCC 6051. The involvement of a common intermediate in the biosynthesis of ikirydinium A and vinblastine is hypothesized.     

Formation of a reversible, intramolecular main-group metal-CO2 adduct

The P,P-chelated stannylene [(i-Pr(2)P)(2)N](2)Sn takes up 2 equiv of carbon dioxide (CO(2)) to form an unusual product in which CO(2) binds to the Sn and P atoms, thus forming a six-membered ring complex. Gentle heating of the solid product releases CO(2), indicating that CO(2) is bound as an adduct to the main-group complex. The groups bound to the CO(2) fragment are not particularly sterically crowded or highly acidic, thus indicating that "frustrated" Lewis acid-base pairs are not required in the binding of CO(2) to main-group elements.     

A problem related to Foulkes’s conjecture

In this paper we study a class of symmetric matricesT indexed by positive integers m≥ n≥2 and defined as follows: for any positive integersp andq let ?_p,q be the set of partitions ofU = {1,2,3, ...,pq} into p blocks each of sizeq. Letm ≥n ≥ 2 be positive integers. By atransversal of α = A₁/A₂/.../A_n ∈ ?_n,m we mean a partitionß = B₁/B₂/.../B_m ∈ ? _m,n such that ‖A _i ∩B _j = 1 for every i= 1,2, ...,n and everyj = 1,2, ...,m. LetM be the zero-one matrix with rows indexed by the elements of ?_n,m and columns indexed by the elements of ?_m,n such that M_αß = 1 iffß is a transversal of α. We are interested in finding the eigenvalues and eigenspaces of the symmetric matrixT = MM^t. The nonsingularity ofT implies Foulkes’s Conjecture (for these values of m andn). In the casen = 2 we completely determine the eigenvalues and eigenspaces of T and in so doing demonstrate the non-singularity ofT. Forn = 3 we develop a fast algorithm for computing the eigenvalues ofT, and give numerical results in the cases m = 3,4, 5, 6.     

Elastic scattering of the carbon isotopes from light nuclei (Z = 7 to 16) in optical model,strong-absorption,and folding approaches

Recently obtained data for elastic scattering of ^12,13C from ¹⁴N, ¹⁶O, ²⁸Si and ³²S are analyzed by a variety of methods, including the conventional six-parameter optical model, Ericson's parameterization of the strong-absorption S-matrix, the Glauber formalism, and a simple single-folding model. It is shown that earlier analyses of similar data, in which the Glauber approach was used exclusively, have a dubious validity.     

Explanation of irregular trend in19F* (I=5/2) nuclear quadrupole interaction in CF4, SiF4, and GeF4

A theoretical investigation of the electric field gradient at excited nuclei¹⁹F^*(I=5/2) of the tetrafluorides CF₄, SiF₄, and GeF₄, has been carried out using the Self-Consistent Charge Extended Hückel procedure to obtain the electronic wave functions. The values of ¦e²qQ¦ that have been obtained are 50.3, 30.4, and 36.3 MHz for CF₄, SiF₄, and GeF₄, respectively, agreeing with the trend in recent experimental data. Physical reasons are presented for the trend, which is irregular as compared to expectations from Townes-Dailey Theory which would have predicted a continuus decrease in going from CF₄ to GeF₄.     

Elastic differential cross sections and analyzing powers for p+40,42,44,48Ca at 0.8 GeV

Differential cross sections and analyzing powers for the elastic scattering of 800 MeV polarized protons from ^40,42,44,48Ca are reported. A first-order, spin-dependent KMT optical potential analysis is presented from which the rms radii of the neutron densities are deduced. A comparison of these results with other determinations and with various theoretical predictions is given.     

Complex microscopic effective interaction for (p,n) reactions

A simple recipe for generating a complex effective interaction for distorted wave Born approximation calculations from a real, microscopic charge-exchange form factor is investigated. The recipe is tested against angular distribution data for ²⁰⁸Pb(p, n) and ²⁰⁹Bi(p, n) from 25 to 50 MeV incident proton energy. The form factor resulting from the recipe is also compared qualitatively to complex effective coupling potentials, resulting from a charge-independent Lane-model formalism and from coupled-channion-channels calculations for a suggested multistep (p, d)—(d, n) reaction mechanism.     

Structural information about tellurium and iodine implanted in semiconductors from analysis of Mössbauer nuclear quadrupole interaction data

We have analyzed through electronic structure investigations, based on a model of an impurity atom trapped close to a substitutional site adjacent to a vacancy, the nuclear quadrupole interactions of¹²⁵Te and¹²⁹I implanted in a number of group IV and III–V semiconductors. Our analysis supports the proposed model for these impurity systems and leads to distances between the impurity and nearest neighbour host atoms close to the normal covalent bond distance, with one exception,¹²⁹I in GaSb, a possible physical reason for which is pointed out. The general nature of our conclusion for the impurity-host bond distances, in particular, its relationship to bond lengths associated with adsorbed halogen atoms at surfaces of semiconductors is discussed.