This revision shortens the sentence and identifies the performers.
However, the original passive style creates parallel structure by repeating the topic of the second sentence ("This structure has...") in the third sentence ("A structure for...").
Notice that the authors used the active voice in the first and second sentences, but the passive in the third.
If the third sentence is changed to active voice, it becomes: Pauling and Corey have already proposed a structure for nucleic acid.
Because active-voice sentences are clearer, livelier, and often more concise than passive-voice sentences, most style guides advise scientific authors to prefer the active voice in their writing.