set outfile [open contacts.dat w]
set numframes [molinfo top get numframes]


for {set i 0} {$i < $numframes} {incr i} {

set mysel [atomselect top "resname DMP and name P OA OB OC OD and within 3.5 of protein" frame $i]
set atomlist   [$mysel get index]
puts "list of atoms within 3 of protein:"
puts "$atomlist"
foreach res $atomlist {
	set rsel [atomselect top "index $res" frame $i]
	set com [measure center $rsel weight [$rsel get mass]]
	puts $outfile "$i Res: $res COM: $com"
	$rsel delete
	}
	}