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MEXICO and MEX

Manual for the MEX/MEXICO program THE McMASTER PROGRAMS FOR EXCHANGE LINESHAPES MEXICO and MEX are programs to calculate the lineshapes of exchanging systems with and without scalar coupling. They are intended to provide a simple way of comparing calculated and experimental lineshapes, so that accurate rate measurements can be made. The programs are an implementation of the theory described in (1). MEX produces the same results as the classic Bloch equations (2,3), but uses the approach that the experimental lineshape is always the sum of individual transitions (4,5). In an NMR spectrum, the intensity of a transition in NMR is given by the product of how much coherence the transition receives from the total z magnetization, times how visible the transition is to the detector. Just as in a normal system, the spectrum of an exchanging system can be viewed as a sum of transitions, but the transition probabilities are complex numbers (1). This is the mathematical method that is also used in the powerful GAMMA program (6). For a coupled spin system, MEXICO uses the same new approach and produces similar results to the durable classic DNMR3 (7). MEX allows great freedom in specifying the exchange mechanism for a system of uncoupled spins, but MEXICO is restricted (at the moment) to two-site exchange with the possibility of unequal populations. Mutual exchange can also be handled. The programs are designed to be run in conjunction with Bruker's XWINNMR program on a Silicon Graphics workstation. This manual has a section on

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