Using Bluez with MDBT42Q.

when I write ... In WebIDE it doesn't give me any hexadecimal character

What does it give you? Maybe try running in the left-hand side of the IDE as that prints the result of evaluating an expression.

You could also use the Linux shell:

echo "LED.toggle()\n" | od -A n -t x1 | tr -d " "

this writes but the led doesn't turn on.

That's odd - I did that it worked for me. Are you definitely using the MDBT42Q, with an up to date firmware? I seem to recall that the original firmware didn't have LED2 defined, so the code might have created an error when it was run.

You could always just do:

NRF.setServices({
  "35ac0001-18b0-e8b7-3feb-62cec301da00" : {
    "35ac0002-18b0-e8b7-3feb-62cec301da00" : {
      value : [0],
      maxLen : 1,
      writable : true,
      onWrite : function(evt) {
        digitalWrite(LED1, evt.data[0]);
      }
    }
  }
});
// and then
 char-write-req 0x0013 01

because we know that the pin LED1 does exist.