Hassan El Khadem, a retired organic chemistry professor who taught at American University, died May 20 at a hospital in Cairo, where he was visiting family. He was 89.

He had heart disease, said his daughter, Samiha Lamerson.

Dr. El Khadem was a chemistry professor at Ohio State University and Michigan Technological University before joining the faculty at American University in 1984.

He was a specialist in carbohydrate chemistry, and he taught classes at American until 1993, when he became an emeritus professor.

Hassan Saad El Khadem was born in Cairo. He received a bachelor’s degree from Cairo University in 1946. He received a doctorate in chemistry from a university in Zurich in 1950, another doctorate in chemistry from Imperial College in London in 1952 and a doctorate from Egypt’s University of Alexandria in 1963. He received a fourth doctorate in chemistry from the University of London in 1967.

He moved to the United States in the late 1960s and had been a resident of Bethesda since the mid-1980s.

His wife of 51 years, Nadia Said El Khadem, died in 2002.

Survivors include two children, Samiha Lamerson of Frederick and Saad El Khadem of Cairo; five grandsons; and a great-grandson.

— T. Rees Shapiro