These are very technical phrases. They seem to mean the same thing. 'characteristcs' and 'properties' here don't seem to have any difference. As chemistry terms, they just refer to things such as acidity, melting and boiling points, reactions with other compounds, form (powder, crystals), etc. You say you regularly encounter them in your work (presumably medicines). I would guess that the information for the medicine/substance either talks about properties OR characteristics, not both, which would suggest they have the same meaning. If you find a medicine/substance which talks about BOTH characteristics AND properties, that would suggest they are different in meaning, in which case you could try posting what each one says to help us understand the difference.

The set of characteristics should be such that the substance may be deduced from that set. They should (together) be a distinctive trait for that specific substance; Of course also the chemical formula is a distinctive trait, but that does not immediately tell about the action that the substance will perform.

The property of a substance is what it contains and how it reacts. The characteristics of a substance are its appearance, mass, etc Potassiums properties : K, 19 Potassiums Characteristics : silvery grey, solid

As two nouns, well, the most effective way I can think of now for you to figure it out is to get an E-Chinese dictionary and see what the Chinese difference is, and that is supposed to be the same difference in E.