There is a scientist I am interested in contacting with expertise in peptidomics. I would like to email them to ask if they had ever explored findings from a related area of research. How do I politely contact them for their input?
First of all, check their personal website and any other content they have published which you have access to which may already offer the input you require. It would certainly be in order to personally e-mail the researcher, but be specific as to the type of input or information you require. The scientist is probably very busy, and a broad question is more likely to go unanswered in that case.
If you intend to refer to certain findings from a related field, ensure you provide all the necessary information to answer your question, or at the very least provide links to the related papers or websites for the convenience of the researcher.
Send them a brief, polite email. Brief because nobody has time to read huge walls of text from strangers; polite because you want them to help you.
Virtually every publication will list a corresponding author along with contact information, usually an email address and/or phone number. All authors are listed with their university and department. You can and should use any or all of this information to find these people and get in touch with the authors of any papers about which you have questions.