denature vs impair

denature

verb
  • To add something to (alcohol) that makes it unsuitable for consumption but leaves it suitable for most other purposes. 

  • To take away a natural characteristic or inherent property of (a thing or a person). 

  • To combine fissile material with nonfissile material in order to prevent its use in an atomic weapon. 

  • To alter its original form or state, especially of a protein, by heat, acidity etc. 

impair

verb
  • To weaken; to affect negatively; to have a diminishing effect on. 

How often have the words denature and impair occurred in a corpus of books? (source: Google Ngram Viewer )