The present invention is directed to acyl and sulfonyl derivatives of 6,9-disubstituted 2–purines of the formula where Z is selected from the group consisting of \u2014S2\u2014, and \u2014C\u2014. This method involves supplying a liquid composition in one or more reservoirs on a rail car, and applying the liquid composition from the one or more reservoirs to the rail surface. The input terminal is connected to one end of the resistor group. The first leg extends substantially parallel to a reference axis. The holder may be configured to hold a single device, or multiple devices aligned in slots defined by partitions. The angling mechanism can include a wedge located between the center of rotation of a centrifuge and a swinging bucket of the centrifuge.