Searching for a Met Opera Singer!
 

Hello everyone,
Our chemistry professor has given us an extra credit problem, but I can't find the answer because I know nothing about opera. I've spent over 2 hours on google already, so I really need your help. Here is the extra credit question:

Who am I?
1. I was a chemist
2. I was a mathematician
3. I was asked to leave high school choir and never return
4. I went on to have a successful career as an opera singer with the N.Y. Met (~50 years)
5. I was still giving guest lectures in math when I died.
6. I changed the spelling of my last name, in part because of WW II anti-German sentiment in America.

I would really appreciate your help.

Thank you.

Google is your friend.