What is the biochemistry of love?
"Love" is a subjective phenomenon that can't really be applied to non-human animals because we can't ask them about their subjective experiences. However there is some clear evidence, especially in more social mammals, of caring behavior and social bonds for other conspecifics.

As far as biological basis, I suppose you could consider it biochemistry, the peptide hormone oxytocin is correlated with formation of social bonds between animals of many species (although Wikipedia isn't the greatest source, you will find this particular page is saturated with links to scientific literature). I would caution against the popular press treatment of oxytocin as "the love hormone" and caution against simplifying a complex set of behaviors to the action of one peptide, but certainly the evolutionary conservation and broad applicability suggest that this is indeed an important hormone in social relationships.