T. J. O'Donnell

UV photoelectron studies of biological pyrimidines: the valence electronic structure of methyl substituted uracils

Abstract UV photoelectron spectroscopy and INDO molecular orbital calculations have been employed to investigate the electronic structure of several methyl substituted uracils. The results indicate that the ionization potential of uracils is most sensitive to perturbation at the 1 and 5 positions. Substitution occurs in both of these positions in biological systems. It is also found that the large (0.4 eV) differences in the ionization potential of uracil and thymine is conserved in the nucleoside models 1-methyluracil and 1-methylthymine.

GRAMPS - A graphics language interpreter for real-time, interactive, three-dimensional picture editing and animation

GRAMPS, a graphics language interpreter has been developed in FORTRAN 77 to be used in conjunction with an interactive vector display list processor (Evans and Sutherland Multi-Picture-System). Several of the features of the language make it very useful and convenient for real-time scene construction, manipulation and animation. The GRAMPS language syntax allows natural interaction with scene elements as well as easy, interactive assignment of graphics input devices. GRAMPS facilitates the creation, manipulation and copying of complex nested picture structures. The language has a powerful macro feature that enables new graphics commands to be developed and incorporated interactively. Animation may be acheived in GRAMPS by two different, yet mutually compatible means. Picture structures may contain “framed” data, which consist of a sequence of fixed objects. These structures may be displayed sequentially to give a traditional frame animation effect. In addition, transformation information on picture structures may be saved at any time in the form of new macro commands that will transform these structures from one saved state to another in a specified number of steps, yielding an interpolated transformation animation effect. An overview of the GRAMPS command structure is given and several examples of application of the language to molecular modeling and animation are presented.

SOME COMPUTATIONAL TRENDS IN THEORETICAL CHEMISTRY

That aspect of the National Resource for Computation in Chemistrys (NRCC) mission directed to advancing the capability of chemists to use computers has led to involvement in efforts to facilitate computations by theoretical chemists. The areas of greatest concentration include algorithm selection and software implementation. Experiences at the NRCC and their implications for the fields of collision dynamics, crystallography, graphics, macromolecular science, quantum chemistry, and statistical mechanics are briefly summarized. A recent study of the reaction of O with C/sub 2/H/sub 4/ is discussed to provide an illustration of progress in the understanding of reaction pathways using computational methods.