The
hydrogen bond is also referred to as hydrogen bridge, and, as its name implies,
it involves a hydrogen atom. Indeed, this is a particular case of a
dipole-dipole interaction (an interaction established between polar molecules) that
includes a hydrogen atom, and requires specific conditions to be established.
There are
two requirements that have to occur in order to be established a hydrogen bond.
Therefore, not all polar molecules having hydrogen atoms have the ability to
establish this type of interaction... The first requirement that must be acomplished
is the existence of a very electronegative atom in one of the involved
molecules. When I say "very electronegative" I 'm referring to one of
the 3 most electronegative atoms - oxygen, nitrogen or fluorine. This atom will
function as an "acceptor" of hydrogen, due to the fact that it is
very electronegative, and thus it will have a very high electron density on it,
presenting a partial negative charge. The second condition that needs to occur
is the existence of a hydrogen atom covalently bonded to a very electronegative
atom. In this case, the latter acts as a "donor" of hydrogen, and the
hydrogen will present partial positive charge because it is attached to a very
electronegative atom.
So, what
happens is an electrostatic attraction between opposite partial charges,
settling the hydrogen bridge. In biochemistry, the hydrogen bonds, like the
remaining non-covalent forces, are very important. The best known example
concerns the interaction between complementary nitrogenous bases in DNA.
And now... despite
having already written this in another post , I can not resist telling it again:
;)
Do you know
how an electron commits suicide?
It jumps
from the hydrogen bridge!
