 The longest residence times have been observed for water molecules near the counterionsthat are localized in the minor groove of the double helix : about 30 ps in the case of Na^{+ K^{+} and Cs^{+} counterions.
<meaning-changed>  The longest residence times have been observed for water molecules near the counterionsthat are localized in the minor groove of the double helix : about 30 ps in the case of Na^{+ K^{+} and Cs^{+} counterions.
 The longest residence times have been observed for water molecules near the counterionsthat are localized in the minor groove of the double helix (about 50 ps for Na^{+ K^{+} and Cs^{+} counterions.