Custom Format a text cell with brackets

Basically I want to surround a text cell with brackets using Format Cells > Number > Custom

From a previous search, I know I can use "("atsymbol")", however that does not preserve superscripts

eg I would like mol m^-3 to be displayed as (mol m^-3) however it comes out as (mol m-3) when using "("atsymbol")"

Is this even possible?

Thanks!

Note I've said 'atsymbol' as it thinks I am trying to post a link when I use that symbol and I'm too new to be permitted to do that