What is the commonality between the antibiotic arsphenamine and azodye ?

Explanation

Arsphenamine is also known as salvarsan. It is synthetic organic aresenic compound that was previously used for treating syphilis. Arsphenamine possess-As=As-linkage.
Azo dyes are used to promote epithelial growth in the treatment of ulcers, burns and other wounds. Many azodyes have anticoagulation action. Azo dyes possess - N = N- linkage like arsphenamine which possess-As = As - linkage.