Taken from http://superuser.com/a/513117/37521

SuperSubMacro.vba

    Sub Super_Sub()
'
' Keyboard Shortcut: Ctrl+Shift+D
'
' If the characters are surrounded by "<" & ">" then they will be subscripted
' If the characters are surrounded by "{" & "}" then they will be superscripted
'
Dim NumSub
Dim NumSuper
Dim SubL
Dim SubR
Dim SuperL
Dim SuperR
Dim CheckSub, CheckSuper as Boolean
Dim CounterSub, CounterSuper as Integer
Dim aCell, CurrSelection As Range

For Each c In Selection
c.Select

CheckSub = True
CounterSub = 0
CheckSuper = True
CounterSuper = 0
aCell = ActiveCell
'
NumSub = Len(aCell) - Len(Application.WorksheetFunction.Substitute(aCell, "<", ""))
    NumSuper = Len(aCell) - Len(Application.WorksheetFunction.Substitute(aCell, "{", ""))
'
If Len(aCell) = 0 Then Exit Sub
If IsError(Application.Find("<", ActiveCell, 1)) = False Then
Do
    Do While CounterSub <= 1000
        SubL = Application.Find("<", ActiveCell, 1)
        SubR = Application.Find(">", ActiveCell, 1)
        ActiveCell.Characters(SubL, 1).Delete
        ActiveCell.Characters(SubR - 1, 1).Delete
        ActiveCell.Characters(SubL, SubR - SubL - 1).Font.Subscript = True
        CounterSub = CounterSub + 1
        If CounterSub = NumSub Then
            CheckSub = False
        Exit Do
        End If
    Loop
Loop Until CheckSub = False
End If
'
'
If IsError(Application.Find("{", ActiveCell, 1)) = False Then
Do
    Do While CounterSuper <= 1000
        SuperL = Application.Find("{", ActiveCell, 1)
        SuperR = Application.Find("}", ActiveCell, 1)
        ActiveCell.Characters(SuperL, 1).Delete
        ActiveCell.Characters(SuperR - 1, 1).Delete
        ActiveCell.Characters(SuperL, SuperR - SuperL - 1).Font.Superscript = True
        CounterSuper = CounterSuper + 1
        If CounterSuper = NumSuper Then
            CheckSuper = False
            Exit Do
        End If
    Loop
Loop Until CheckSuper = False
End If
'
Next

End Sub