Dynamically bind value in ngClass

Question

how can i dynamically add value in ngClass?. I have a variable named labelClass in the component file now i want to add that in ngClass.I tried to do using interpolation but getting parsing error so how can i dynamically bind the value to attribute?

<label for="fddTimeslot" 
       class="control-label" 
       [ngClass]="{'col-lg-4 col-xs-8' : !labelClass, {{labelClass}}: 
                  !!labelClass}"> {{label}} 
</label>

Error:

Parser Error: Got interpolation ({{}}) where expression was expected 
at column 36 in [{'col-lg-4 col-xs-8' : !labelClass, {{labelClass}}: !!labelClass}] 
in ng:///AppModule/FilteringDropdownListSelectorComponent.html@12:18
("SelectorActionButton}"> 
   <label for="fddTimeslot" 
          class="control-label"
          [ERROR ->][ngClass]="{'col-lg-4 col-xs-8' : !labelClass,
                               {{labelClass}}: !!labelClass}">
                               {{label}"): 
      ng:///AppModule/FilteringDropdownListSelectorComponent.html@12:18