As to (hususunda, mevzuunda, gelince)

As to his ability, we are sure that he can do the job.
Onun kabiliyetine gelince, eminiz ki işi yapabilir.

We have no news as to his health.
Onun sıhhatine dair haberimiz yok.

We have not any information as to his political ideas.
Onun siyasî fikirlerine ait herhangi bir malûmatımız yok.