Richard D. Cornelius

Cobalt(III)-promoted hydrolysis of atp

Abstract The rate of phosphate hydrolysis of ATP in the substitution-inert complex Co(NH3)4ATP-has been examined in the presence and absence of [Co(cyclen)(H2O)2]3+. The rate of hydrolysis of Co(NH3)4ATP- in the absence of [Co(cyclen)(H2O)2]3+ is essentially independent of pH in the range 6.0 to 9.0, and the rate constant is 2.6 × 10−5 sec −1 at pH 9.0, 40°C, and 1.0 M ionic strength Rate constants for the hydrolysis of Co(NH3)4ATP- in the presence of [Co(cyclen)(H2O)2]3+ are sharply dependent upon pH in the same range. The rate constants at pH 8.0, 8.6, and 9.0 are 8, 63, and 95 times larger than the rate constant at pH 7.0. At pH 9 the rate constant is 1.2 × 10−3 sec−1 for 16 mM Co(NH3)4ATP- in the presence of 10 mM [Co(cyclen)(H2O)2]3+. The proposed mechanism for hydrolysis involves the coordination of a phosphate group of Co(NH3)4ATP- by [Co(cyclen)(H2O)2]3+ to form a dinuclear species, followed by internal attack of coordinated hydroxide on the phosphate chain.

A heuristic problem solver: GEORGE

Abstract Developing problem solving skills is an important educational objective in science teaching. In conventional applications of Computer-Assisted Learning, students are trained through tutorials, drill and practice, guided problems and simulation. One obstacle in the way of achieving a high degree of individualization is that the computer has been unable to answer questions for which answers have not been encoded. The use of artificial intelligence techniques and in particular of expert systems, may remove this obstacle. The program described here constitutes one step in this direction. The program is called GEORGE and has some of the essential characteristics of expert systems. It has been designed to find the solution to most problems of elementary chemistry dealing with mass, volume and number of moles. Contrary to conventional algorithmic programs which deal repeatedly with similar data and always process them in the same way, GEORGE uses heuristic rules to discover a solution to a problem. The program has no questions to offer students but shows users how to solve problems of their own. The heuristic rules are very simple and can be understood by students. In order to use this program, a student must be able to define precisely the quantity which is to be found and to identify the available data. If the available data are insufficient to support a solution, the program tells the user and asks for data relating to the missing information. If the data are sufficient, the program supplies the answer, but more important is that it explains how the answer was reached. Diagrams are used to show the network relating the available items of information to the solution. If the student finds some problems especially interesting. these problems can be saved to be used again or even modified for later use. Thus the student can create a personal collection of problems. This approach is different from traditional categories of Computer-Assisted Learning. The possible impact of creating and using problem solvers in science education is discussed.