# Copyright (c) 2002-08 Peter Guntert. All rights reserved.
## 7MACROS: hbond - CYANA macro
##
## Parameters: atom1=<string>                 (required)
##             residue1=<integer>             (required)
##             atom2=<string>                 (required)
##             residue2=<integer>             (required)
##
## Creates the standard upper and lower limit distance restraints
## (Williamson et al., 1985) to enforce a hydrogen bond between two atoms,
## one of which must be a hydrogen atom. The distance between the hydrogen
## and the acceptor is restrained to the range 1.8-2.0 A, and the distance
## between the atom covalently bound to the hydrogen and the acceptor is
## restrained to the range 2.7-3.0 A.

var info echo i i1 i2

syntax $macro:atom1=* residue1=@i atom2=* residue2=@i

info:=none; echo:=off
do i 1 2
  i$i=iatom('$atom$i $residue$i')
  if (i$i.le.0) error "Atom $atom$i $residue$i does not exist."
end do
if (element(i2).eq.1) then
  i=i1; i1=i2; i2=i
end if
if (element(i1).ne.1) error "No hydrogen atom in hydrogen bond."
i=ibond(i1,1)
distance make "$atom(i1)" "$atom(i2)" lol=1.8 upl=2.0
distance make "$atom(i)"  "$atom(i2)" lol=2.7 upl=3.0
unset info
print "    Restraints for hydrogen bond $atomlong(i1) - $atomlong(i2) added."