As one can see that the books on left do not remain straight after few days. They become inclined. This affects the bottom corner of book, it gets folded with a large radius.
The normal solution is to use bookends:
(random image picked from a 'bookends' image search)
You can buy these, but you can also build them yourself. One option is to get a few pieces of wood in A4 size and attach them to the wall (or to your existing shelf on the left) vertically, then insert the books and binders between them.