The validity of the “few-level” approximation in gaseous relaxation phenomena

The Bloch equations including damping are formulated for a molecular system excited by incident radiation. In contrast with a previous treatment the present formalism gives an intuitively satisfactory form of relaxation terms. A three-level system irradiated by a single oscillating field is specifically considered, and using this manifold as a model for a two-level system immersed in a heat bath, the problem of “embedding” a pair of levels connected by radiation within a multi-level manifold is treated. A brief discussion of transient solutions to the Bloch equations is included.     

The variation of speckle size with film density: An example of Babinet's principle

The variation of the size of photographically recorded laser speckle with film density is compared with the predicted speckle size. The ten percent increase in the recorded speckle size and high average film densities is due to the non-linear film response and is an example of Babinet's Principle.     

Irreversible enzyme inhibitors. LXXXIX. candidate active-site-directed irreversible inhibitors of dihydrofolic reductase. X. derivatives of 2-amino-5-benzamidopropyl-4-pyrimidinol

Since 2-amino-5-benzamidopropyl-6-methyl-4-pyrimidinol (VII) was a reasonably good reversible inhibitor of dihydrofolic reductase, the benzamido group was substituted with p-bromomethyl (XVIIa), m-bromomethyl (XVIIIa), and p-bromoacetyl (XIXa) groups; these compounds, and the corresponding 6-phenylpyrimidines, were synthesized from the proper 2-amino-5-aminopropyl-4-pyrimidinol (V) by devising methods that were compatible with the high reactivity of the halogen. Compounds XVII-XIX showed in-activation of dihydrofolic reductase; the fact that p-nitrobenzyl bromide inactivated the enzyme as rapidly as XVII and XVIII and phenacyl bromide inactivated the enzyme as rapidly as XIX indicated that these inactivations proceeded by a random bimolecular mechanism and not the desired active-site-directed mechanism.     

Lithium insertion into Co3O4: A preliminary investigation

Lithium has been inserted into the spinel Co₃O₄ both chemically and electrochemically. During lithiation the tetrahedral A-site Co²⁺ cations are displaced into neighbouring empty octahedral sites: the incoming Li⁺ ions occupy the remaining interstitial octahedra of the spinel structure to produce the partially ordered rocksalt compound LiCo₃O₄. The octahedral B-site cations of the A[B₂]X₄ spinel are unperturbed by this reaction: the oxide lattice expands by 8.6%. Lithium analyses and powder X-ray diffraction spectra indicate that further lithiation is possible. However, it is demonstrated that a fast lithiation in excess of LiCo₃O₄ is followed by a slow extrusion of B-site cobalt at 50°C until all the Li on the 8a sites has moved to the octahedral vacancies thus created.     

Mass spectra of synthetic mitosenes

The mass spectral fragmentation of a series of 10 mitosene analogs is described. Major pathways arise through decomposition of the substituents in the 1 and 10 positions and are unaffected by the substituent in the 7 position. The base peak in the spectrum, in most cases, is represented by the basic mitosene ring. The patterns are general for this series of compounds and may have application in elucidating the structure of the DNA alkylation sites involved in reactions with mitosenes or natural mitomycins.