Core, nucleus

There is no clear rigorous definition of an atom in a molecule in conventional bonding models. In the Lewis model an atom in a molecule is defined as consisting of its core (nucleus and inner-shell electrons) and the valence shell electrons. But some of the valence shell electrons of each atom are considered to be shared with another atom, and how these electrons should be partitioned between the two atoms so as to describe the atoms as they exist in the molecule is not defined. 

A brominated pyrrole-imidazole alkaloid, rac-dibromophakellstatin, has been shown to display selective antitumor activity in vitro with the highest activity on the ovarian cancer cell line OVXF 899L <2007BMCL346>. The chemistry and bioactivity of anti-tubulin agents, either natural or synthetic, having an indole as core nucleus have been reviewed <2007MI209>. 

There is no information on the site of formation of the Fe(III)-0-Fe(III) dimers that have been observed in rHF as well as in horse spleen ferritin (57,112). This may be clarified by Mossbauer spectroscopy on ferritin variants. Possible positions are the putative nucleation center or the double Tb site. In the latter case, either the dimers themselves must move or the iron core nucleus must incorporate iron atoms from the ferroxidase centers. Because ferrihydrite can be deposited both in rLF and in the rHF variant lacking ferroxidase activity, nucleation at this center is not possible for these molecules. Indeed, a specific center may not be required. However, electron micrographs of broken ferritin molecules suggest an attachment of ferrihydrite to the protein shell (113). 

The core nucleus of the mitomycinlike antitumor agent FR-900482 was synthesized by F.E. Ziegler and co-workers. The selective oxygenation of the C9a position was achieved by the Polonovski reaction. 

In the laboratory of F.E. Ziegler, the synthesis of the core nucleus of FR-900482 was accomplished. In the final stages of the synthetic effort, the removal of the formyl group from the C7 quaternary center was necessary. The authors chose the Tsuji-Wilkinson decarbonylation protocol to effect the transformation. The 1,3-diol functionality was protected as the acetonide prior to the decarbonylation. Usually the rate of decarbonylation is slowest for aldehydes that have the formyl group attached to a quaternary carbon, so it was necessary to use more than two equivalents of the catalyst to effect the decarbonylation at the reflux temperature of xylene. 

In the laboratory of F.E. Ziegler, the cyclization of a chiral aziridinyl radical into an indole nucleus was utilized to prepare the core nucleus of the potent antitumor agent FR-900482. In the early stages of the synthetic effort, the VUsmeier-Haack formylation was chosen to install an aldehyde functionality at the C3 position of a substituted indole substrate. The initial iminium salt was hydrolyzed under very mildly basic conditions to minimize the hydrolysis of the... 

Ziegler, F. E., Belema, M. Chiral Aziridinyl Radicals An Application to the Synthesis of the Core Nucleus of FR-900482. J. Org. Chem. 

In case of large overlapping or mutually penetrating cores a core-core repulsion correction (CCRC) to the point charge repulsion model in Eq. 27 is needed. A similar core-nucleus repulsion correction (CNRC) has to be applied for the interaction between nuclei of atoms treated without ECP and centers with large-core ECPs. A Bom-Mayer type ansatz proved to be quite successful to model the pairwise repulsive correction [206,207]... 

What soon emerged was a nuclear model of the atom, first proposed by New Zealand-bom physicist Ernest Rutherford. In this view, an element s identity was determined by its atomic number, the amount of positive charge in the very small core nucleus that also contained almost all of the atom s mass. The light electrons were held in orbits by electrostatic attraction to the positive core. 

R. J. Jones and H, Rapoport, Enantiospecific synthesis of an aziridinobenzoazocinone, an advanced intermediate containing the core nucleus of Fr900482 and Fk973, J. Org. Chem., 55 (1990) 1144-1146. 

Ziegler has demonstrated the successful cyclization of an aziridinyl radical onto the C-2 position of potentially labile indole-3-carbinol derivative 124 as the key step in an asymmetric route to the core nucleus (e.g., 125) of the antitumor agent FR-900482 <97JOC1083>. 

Ziegler FE, Belema M (1997) Chiral aziridinyl radicals an application to the synthesis of the core nucleus of ER-900482. J Org Chem 62 1083-1094... 

The MNDO v ence-electron Hamiltonian H is given by (16/83) and the Fock matrix elements are given by (16.84). As in (16.85), the core Hamiltonian operator for valence electron 1 is written as H° °(l) = - jV -I- EbVb(1)> where Ya(l) is the part of the potential energy of electron 1 due to its interactions with the core (nucleus plus inner-shell electrons) of atom B. To evaluate the Fock matrix element in (16.84), we... 

The pairing interaction gives rise to powerful cluster formation on the nuclear surface, therefore, far from the double magic core nucleus it is reasonable to use the BCS... 

In this context, an atomic system is composed of a core (nucleus + internal electrons) found at the (virtual) cubic center and a layer of valence (the external atom) with the electrons symmetrically disposed toward the core in the cube s comers, so that a maximum symmetry to the cube center to be covered, see Figme 3.1. 

FR-900482 918, a mitomycin-like antitumor agent, isolated from Streptomyces sandaensis, exists as a 2 1 mixture f> a ether bridge) of stereoisomers at neutral pH, but almost exclusively as the j8-isomer in acidic media. An asymmetric route to its core nucleus involves the cyclization of an aziridinyl radical derived from 914 to give a functionalized indole nucleus 915 —> 916. In a further step, a bmzyloxy-carbonyl group is introduced on the primary alcohol function using CDI and benzyl alcohol, affording 917 in 71% yield [659]. 

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